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C 1 R  C  UL  A  TING    B  R  A  XCH. 


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SCIENCE 


X 


FOR  THE 


SCHOOL   AND  FAMILY. 

PART   III. 

MINERALOGY  AND  GEOLOGY. 


BY 


WORTHINGTON  HOOKER,  M,D,, 

PEOFE8SOB  OF  THE  THEORY  AND  PRACTICE  OF  MEDICINE  IN  YALE  COLLEGE, 

AUTHOR  OF  "HITMAN  PHYSIOLOGY,"  "CHILD'S  BOOK  OF  NATURE," 

"NATURAL  HISTORY,"  &C. 


KllustratetJ  fc£  nearlg  gtoo  ffitmfrtefr 


NEW    YORK: 
HARPER   &    BROTHERS,    PUBLISHERS, 

FRANKLIN    SQUARE. 
1    865. 


•x 

LIBRARY 

By  Dr.  Worthington  Hooker. 


The  Child's  Book  Of  Nature.  For  the  Use  of  Families  and  Schools;  in- 
tended to  aid  Mothers  and  Teachers  in  training  Children  in  the  Observation  of 
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PART  I.  PLANTS. 

PAETII.  ANIMALS. 

PABT  III.  AIR,  WATER,  HEAT,  LIGHT,  &c. 

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Science  for  the  School  and  Family. 

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PART  II.  CHEMISTRY.     Illustrated  by  numerous  Engravings.     12mo, 
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PART  III.  MINERALOGY  AND  GEOLOGY.    Illustrated  by  numerbus. 
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Published  by  HARPER  &  BROTEERS,  Franklin  Square,  N.  Y. 


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/ 


PREFACE. 


THIS  book  is  intended  to  meet  the  wants  of  beginners  in  the  study 
of  Geology,  and  especially  young  beginners.  There  are  many  ele- 
mentary books,  so  called,  on  this  science,  but  they  all,  so  far  as  I 
have  seen  them,  contain  much  matter  which  is  suited  only  to  those 
who  have  already  become  acquainted  with  the  subject.  They  cover 
too  much  ground  for  a  beginner.  And,  besides  this,  they  are  not 
sufficiently  simple  in  their  explanations  and  illustrations.  These 

defects  I  have  endeavoreehto  avoid  -in  the  construction  of  this  book. 

»_•  . 
My  object  has  been  to  produce  a  text-book  fitted  to  prepare  those 

who  are  wholly  unacquainted  with  the  subject  for  the  farther  study 
of  it  in  the  books  of  professed  geologists.  I  would  gladly  have  left 
this  task  to  some  of  them,  but,  as  no  one  has  met  the  existing  want, 
I  have  undertaken  to  do  it,  though  with  some  hesitation,  from  my 
lack  of  familiarity  with  the  full  minutiae  of  the  subject.  But  per- 
haps the  fact  that  I  have  been  obliged  to  be,  to  some  extent,  a  learn- 
er, in  order  to  accomplish  my  task,  has  the  better  fitted  me  for  it,  as 
I  have  thus  become  sensible  of  the  wants  of  the  learners  for  whom 
I  write. 

As  in  my  Chemistry  (Part  II.),  so  in  this  book,  I  have  made  it  a 
point  to  convey  to  the  pupil  simply  that  knowledge  of  the  study 
which  every  well-informed  person  ought  to  possess,  leaving  out  those 
minutiae  which  are  of  value  only  to  one  who  intends  to  be  a  thorough 
geologist.  I  have  also  brought  out  very  prominently  those  common 
geological  phenomena  which  are  within  the  scope  of  ordinary  ob- 
servation, so  that  the  pupil  may  be  prompted,  by  what  he  learns  in 


IV  PBEFACE. 

this  book,  to  prosecute  his  observations  and  investigations  in  his 
daily  walks,  and  in  his  travels  to  different  localities,  far  or  near. 

I  do  not  go  largely  into  Mineralogy,  but  present  enough  of  it  sim- 
ply to  prepare  the  pupil  for  the  study  of  Geology.  Observe  in  this 
connection  the  natural  succession  of  subjects  in  the  three  parts  of 
this  portion  of  my  series.  The  Natural  Philosophy  properly  pre- 
cedes the  Chemistry,  and  this  latter  the  Mineralogy  and  Geology, 
each  study  preparing  the  pupil  to  understand  what  comes  after.  It 
should  be  remarked  here  that  these  studies,  together  with  that  of 
Zoology,  should  precede  the  study  of  Physical  Geography,  for  ac- 
quaintance with  them  is  absolutely  essential  to  any  thing  like  a  full 
knowledge  of  that  science  ;  and  yet  it  is  very  common  to  see  class- 
es wearily  plodding  through  some  book  on  Physical  Geography, 
who,  from  lack  of  this  preparation,  find  most  of  it  a  terra  incognita, 
and  know  but  little  of  what  they  have  passed  through  when  they  ar- 
rive at  their  journey's  end.  Let  me  not  be  understood  to  say  that 
this  science  should  not  be  studied  at  all  till  after  the  pupil  has  gone 
through  with  the  "Studies  that  I  have  mentioned.  It  is  only  the  full 
consideration  of  it  that  should  be  delayed  till  that  period.  It  should 
be  introduced,  more  or  less,  throughout  the  whole  previous  course, 
mingled  with  the  teaching  of  Geography  as  it  is  now  ordinarily  pur- 
sued. But  this  can  not  be  done  properly  and  effectually  unless  the 
study  of  the  natural  sciences  be  made  a  part  of  education  from  the 
outset,  as  is  contemplated  in  my  series  of  books,  beginning  with  the 
"Child's  Book  of  Common  Things,"  and  ending  with  the  present 
work.  That  this  view  of  the  matter  is  correct  is  readily  seen  if  you 
observe  how  tributary  are  the  natural  sciences  to  the  interest  and 
value  of  the  study  of  Geography,  for  without  their  contributions  to 
it  this  branch  is  nothing  more  than  mere  dry  topography  and  sta- 
tistics. 

The  materials  for  this  book  I  have  drawn  from  various  sources. 
Foremost  stand  the  works  of  Professor  Dana,  and  especially  that 


PREFACE.  V 

grand  American  book,  his  Manual  of  Geology.  Then  there  are  the 
books  of  Lyell,  Hitchcock,  Hugh  Miller,  Phillips,  Gray  and  Adams, 
Kichardson,  etc.  I  mention  with  special  pleasure  some  smaller 
works  from  the  English  press.  "The  Past  and  Present  Life  of  the 
Globe,"  by  Page,  is  a  most  able  and  interesting  commentary  on  the 
life-record  of  the  earth's  formation.  "  Geology  in  the  Garden,"  by 
Rev.  Henry  Eley,  shows  in  a  very  ingenious  manner  what  may  be 
learned  about  English  Geology  by  following  out  the  suggestions  de- 
rived from  the  examination  of  the  soil  of  a  garden.  One  of  the 
best  books  for  a  beginner  that  I  have  met  with  is  the  "  School  Man- 
ual of  Geology, "by  Mr.  Jukes,  local  director  of  th*e  geological  sur- 
vey of  Ireland.  It  would  be  well  for  the  teacher  to  have  some  of 
the  books  which  I  have  mentioned  for  the  purpose  of  reference,  so 
that  he  may,  if  he  wishes,  bring  up  additional  matter  in  his  teach- 
ing, or  answer  any  inquiries  of  his  pupils  on  points  that  may  not  be 
fully  treated  in  this  book.  This  would  be  in  consonance  with  the 
principles  I  laid  down  in  the  preface  to  my  Natural  History  in  regard 
to  the  relative  use  of  text-books  and  books  for  reference. 

I  may  say  of  this  book  as  I  said  of  Part  II.,  that  in  the  present 
state  of  education  it  is  adapted  to  high  schools  and  academies ;  and 
yet  it  would  be  within  the  grasp  of  the  older  pupils  of  our  common 
schools  if  they  had  studied  in  their  proper  time  all  the  other  books 
of  the  series,  for  this  is  no  greater  height  than  is  reached  in  some 
other  branches,  where  all  the  steps  of  the  gradation  are  taken  from 
the  beginning,  as,  for  example,  in  Mathematics. 

That  such  studies  as  are  provided  for  in  the  series,  of  which  this 
is  the  concluding  book,  should  be  pursued,  to  some  extent,  before 
arriving  at  the  high  school  or  the  academy,  is  very  clear,  if  you  con- 
sider the  fact  that  the  majority  of  pupils  end  their  education  when 
they  pass  from  the  higher  classes  of  the  common  school.  Most  of 
these  engage  in  various  arts  and  trades,  and  so  have  to  do  constantly 
in  the  business  of  their  life  with  the  principles  that  are  learned  in 


V  PREFACE. 

these  studies.  Why,  then,  should  not  these  principles  be  taught  to 
them,  it  is  pertinent  to  ask,  if  it  be  the  great  object  of  education  to 
prepare  one  to  act  well  his  part  in  life  ?  And  in  the  case  of  those 
who  are  not  to  pursue  any  art  in  which  the  principles  of  natural 
science  are  brought  into  play,  a  knowledge  of  the  phenomena  that 
abound  around  us  in  air,  water,  and  earth  is  not  only  valuable  as 
information,  and  as  a  source  of  enjoyment,  but  also  as  a  means  of 
mental  culture. 

The  questions  in  this  and  the  previous  parts  I  have  put  at  the  end 
of  the  book,  believing  that  when  they  are  nearer  to  the  text  both 
pupil  and  teacher  are  apt  to  depend  on  them  too  much.  For  this 
reason  also  I  have  the  numbers  refer  to  the  pages,  while  in  the  Index 
I  have  the  more  definite  reference  to  the  paragraphs.  In  the  Glos- 
sary there  are  no  definitions,  but  references  to  paragraphs  where  the 
explanation  of  the  terms  can  be  found.  W.  HOOKER. 

January,  1865. 


CONTENTS. 


CHAPTER  PAGE 

I.    MINERAL   SUBSTANCES 9 

II.    CONSTRUCTION   OF   MINERALS.. 14 

III.  CARBON  AND   ITS   COMPOUNDS 23 

IV.  SULPHUR   AND   ITS   COMPOUNDS 33 

V.   METALS   AND  THEIR   ORES 39 

VI.    OXY-SALTS   AND   HALOID    SALTS 49 

VII.    EARTHY    MINERALS 56 

VIII.    ROCKS 67 

IX.    THE   EARTH   AS   IT  IS 79 

X.    PRESENT   CHANGES   IN   THE   EARTH 90 

XI.    CONSTRUCTION   OF   THE   EARTH 123 

XII.    RECORD   OF   LIFE   IN  THE   ROCKS 160 

XIII.  AZOIC   AGE 181 

XIV.  AGE   OF   MOLLUSKS 187 

XV.    AGE   OF   FISHES 201 

XVI.    AGE   OF   COAL 213 

XVII.    AGE    OF   REPTILES 236 

XVIII.   AGE   OF    MAMMALS 261 

XIX.    AGE   OF   MAN 305 

XX.    CONCLUDING   OBSERVATIONS 314 


SITZ 


MINERALOGY  AND  GEOLOGY, 


CHAPTER  I. 

MINERAL   SUBSTANCES. 

1.  Different  Forms  of  Minerals. — As  solid  substances 
alone  are  kept  in  mineral  cabinets,  minerals  are  thought 
of  by  most  people  as  being  only  in  the  solid  form.     But 
there  are  mineral  liquids  and  gases.    Mercury  is  a  liquid 
mineral.     Water  is  a  liquid  composed  of  two  mineral 
gases,  oxygen  and  hydrogen.    The  atmosphere  is  a  mix- 
ture of  three  mineral  gases — oxygen,  nitrogen,  and  car- 
bonic acid,  and  holds  always  in  solution  some  of  a  min- 
eral liquid — water.    All  minerals  are,  in  one  sense,  solid, 
for  the  atoms  of  which  liquids  and  gases  are  composed 
are  solid.    All  matter  is  undoubtedly,  as  Newton  sup- 
posed, formed  of  "  solid,  massy,  hard,  impenetrable  par- 
ticles" (Part  I.,  §  14). 

2.  Relation  of  Heat  to  the  Forms  of  Matter. — The  form 
which  many  mineral  substances   assume  is  dependent 
upon  the  degree  of  temperature  to  which  they  are  ex- 
posed.    Thus  water  appears  in  the  three  forms — solid, 
liquid,  and  gaseous,  according  to  the  degree  of  heat. 
We  ordinarily  speak  of  it  as  a  liquid  substance,  because 
under  all  ordinary  circumstances  it  has  this  form ;  but 
there  are  localities,  as  the  tops  of  some  mountains  and 
the  extreme  polar  regions,  where  its  ordinary  condition 
is  that  of  a  solid.    For  the  same  reason,  we  speak  of 
metals,  with  the  exception  of  mercury,  as  solids ;  but 
there  was  a  time,  in  ages  long  gone  by,  as  you  will  see 
in  the  geological  part  of  this  book,  when  these  metals 

A  2 


10  MINERALOGY. 

were  in  a  liquid  state,  and,  with  such  a  degree  of  heat  as 
prevailed  then,  the  water  must  have  been  in  the  vapor- 
ous form.  Some  of  the  gases  have  been  reduced  to  a 
liquid  and  even  a  solid  state  by  the  combined  influence 
of  cold  and  pressure,  and  some  have  been  made  liquid 
by  cold  alone. 

3.  Substances  which  are  Not  Mineral. — Those   sub- 
stances are  not  considered  mineral  which  have  been  pro- 
duced by  living  agencies.     They  are  of  three  kinds:  1. 
Organized  substances,  or  those  which  are  found  in  the 
structures  of  animals  and  vegetables.     These  are  called 
organized  because  they  have  organs  in  them,  as  sap-ves- 
sels, blood-vessels,  etc.    Their  mode  of  growth  or  in- 
crease is  different  from  that  of  minerals,  for  minerals  in- 
crease by  additions  wholly  upon  the  outside,  while  or- 
ganized substances  grow  at  every  point,  internally  as  well 
as  externally,  by  the  circulation  in  their  organs.    2.  Sub- 
stances contained  in  living  organs,  being  formed  by  them, 
as  starch,  sugar,  fats,  etc.     3.  Substances  which  come 
from  certain  changes  in  those  of  the  first  and  second 
classes,  as,  for  example,  alcohol  produced  from  sugar. 
For  a  more  full  exposition  of  this  subject  I  refer  you  to 
Chapter  XIX.  of  Part  II. 

4.  All  Matter  Once  Mineral. — There  was  a  time  when 
there  was  no  life  on  this  earth  of  ours,  and,  therefore,  all 
the  matter  was  mineral.    This  is  indicated  in  the  Mosaic 
account  of  the  creation,  for  vegetable  and  animal  life 
were  introduced   after  certain  preparations  had  been 
made  for  them ;  and  what  is  thus  indicated  has  been  de- 
monstrated to  be  true  by  the  examination  of  the  rocks 
by  geologists,  as  you  will  see  hereafter.     This  lifeless 
period  occupied  a  long  series  of  ages.    All  this  time  no 
organic  substances  were  formed,  for  life  always  presides 
over  their  formation,  using,  indeed,  such  agencies  as  heat, 
light,  and  chemical  action,  but  directing  and  controlling 
them.     (Part  II.,  §  509.) 

5.  Life  Introduced  by  the  Creator. — When  the  earth 


MINEEAL    SUBSTANCES.  11 

was  brought  to  a  proper  state  for  the  agencies  of  life, 
then,  and  not  till  then,  was  life  introduced  by  the  Crea- 
tor upon  the  stage  of  action.  Then  the  mineral  matter 
in  earth,  water,  and  air  began  to  be  acted  upon  by  the 
new  agencies,  and  there  were  evolved  living  forms,  veg- 
etable and  animal.  And  these  forms  were  capable  of 
producing  substances  which  no  mere  chemical  action  of 
the  mineral  atoms  was  able  to  produce  during  all  the 
long  lifeless  ages  of  the  world,  or  during  the  long  ages 
since.  The  elements  of  which  starch,  sugar,  fat,  etc.,  are 
composed,  have  been  in  existence  ever  since  the  matter 
of  our  world  was  first  created,  and  they  exist  now  abun- 
dantly in  the  air  and  water ;  and  yet,  though  they  have 
always  been  acting  upon  each  other,  never  have  they 
been  able  so  to  combine  as  to  produce  these  substances, 
unless  life  come  in  to  direct  their  action.  Life  is  contin- 
ually evolving  new  forms  and  substances  from  dead  min- 
eral matter,  which  in  the  change  it  endows  with  proper- 
ties that  it  did  not  before  possess. 

6.  Decay. — In  what  is  termed  the  decay  of  animal  and 
vegetable  substances,  we  have  the  opposite  of  the  proc- 
esses alluded  to  in  §  5.  Here  we  have  a  return  of  living 
substances  to  the  state  of  dead  mineral  matter.  There 
is  no  actual  decay — that  is,  no  real  loss  of  matter,  but 
merely  change  in  the  relations  of  the  atoms  which  com- 
pose the  substances.  Life  has  let  go  its  control,  and  the 
atoms  obey  the  common  laws  of  chemistry.  For  exam- 
ple :  an  egg  has  life  in  it,  and  that  life,  with  the  aid  of 
a  proper  degree  of  heat,  evolves  within  that  prison  of 
chalk  a  complicated  living  form — a  bird  ;  but  let  that 
life  in  some  way  be  destroyed,  and  chemical  action  at 
once  begins  its  work,  returning  the  matter  to  the  min- 
eral world  by  combinations  of  its  atoms  in  new  forms. 
One  of  these  combinations,  for  example,  is  a  gas,  which 
is  the  cause  of  the  peculiarly  disagreeable  odor  of  a  de- 
caying egg — sulphureted  hydrogen,  resulting  from  the 
union  of  sulphur  with  hydrogen  gas. 


1 2  MINERALOGY. 

7.  Mineral  Matter  in  Vegetables  and  Animals. — Or- 
ganic substances  are   not  wholly  destitute  of  mineral 
matters,  and  some  have  large  quantities  of  such  matter 
in  them.     There  is  silica  or  flint  in  plants,  especially  in 
the  grasses ;  but  this  is  one  of  the  most  extensively  dif- 
fused of  minerals,  making  up  most  of  the  sand  of  the 
earth,  entering  largely  into  the  composition  of  granite 
and  other  rocks,  and  being  more  or  less  mingled  up  with 
the  common  earth  every  where.     Then  there  is  carbon- 
ate of  lime,  the   mineral   which   constitutes  the  lime- 
stones, the  chalks,  and  the  marbles,  making  up  the  shells 
of  the  shell-fish  and  the  skeletons  of  the  coral  animals ; 
and  phosphate  of  lime  is  the  chief  constituent  of  bone. 
But,  in  these  and  all  other  similar  cases,  there  is  mere 
deposition  of  mineral  matter  in  interstices  in  the  living 
organs,  and  no  real  change  of  it  into  living  matter. 

8.  Rocks  Formed  from  the  Mineral  Substances  in  Ani- 
mals.— Quite  a  large  portion  of  the  rocks  in  the  earth 
have  been  formed  from  the  mineral  remains  of  animals. 
It  is  supposed  by  some  geologists  that  this  is  true  of  all 
which  are  composed  of  carbonate  of  lime.     It  is  at  least 
extensively  true  of  them,  as  we  know  by  the  remains  of 
shells  and  corals  found  in. them.     Much,  if  not  all,  the 
marble  in  the  world  was  once  a  conglomerate  of  such 
remains,  and  was  crystallized  into  its  beautiful  granular 
condition  chiefly  by  the  agency  of  heat.     So,  also,  some 
flinty  rocks  are  formed  from  the  silica  of  the  shields  or 
skeletons  of  animals  and  vegetables,  for  the  most  part 
exceedingly  minute  in  size.     It  is  thus  that  these  liv- 
ing forms  gather  from  the  water  in  which  they  live  ma- 
terial for  their  structure,  which,  when  they  die,  is  laid 
down  to  be   consolidated  into  rock.     This  interesting 
subject,  barely  touched  here,  will  be  fully  treated  of  here- 
after. 

9.  Minerals  Simple  and  Compound.  —  Some  minerals 
are  found  in  nature  in  their  simple  elementary  state 
alone,  while  others  are  found  only  in  combination  with 


MINERAL   SUBSTANCES.  13 

other  elements,  and  others  still  are  found  in  both  condi- 
tions. I  will  give  some  examples  of  each.  Some  of  the 
noble  metals  (so  called),  as  gold  and  platinum,  are  never 
found  combined  with  any  other  element.  On  the  other 
hand,  the  metals  potassium,  sodium,  calcium,  magnesium, 
aluminum,  and  ammonium  are  never  found  uncombined. 
Silver,  copper,  and  mercury  are  among  the  examples  of 
metals  that  are  found  in  their  simple  state,  or,  as  it  is 
commonly  expressed,  found  native,  and  also  combined 
with  other  elements,  as  sulphur,  oxygen,  etc.,  in  the  form 
of  ores.  While  oxygen  is,  in  its  simple  state,  in  the  mix- 
ture which  we  call  air,  it  also  appears  in  combination 
with  almost  all  the  elements,  and  forms  from  one  third 
to  one  half  of  the  crust  of  the  earth.  Hydrogen,  which 
is  so  abundant  as  one  of  the  elements  of  water,  is  never 
found  uncombined.  The  same  may  be  said  of  chlorine, 
one  of  the  elements  of  common  salt.  Sulphur  and  car- 
bon are  both  found  native  as  well  as  combined,  but  phos- 
phorus is  always  in  combination. 

10.  Minerals  that  Contain  Many  Elements. — There  is 
very  great  difference  in  degree  in  the  compound  char- 
acter of  the  minerals  found  in  mineralogical  cabinets. 
While  there  are  many  of  those  compounds  which  were 
brought  to  your  notice  in  Part  II. — oxyds,  sulphurets, 
salts,  etc. — there  are  also  many  which  are  much  more 
compound  than  these.     The  only  approach  made  to  such 
complex  compounds  by  the  processes  of  chemistry  is  in 
the  double  salts,  such  as  alum,  and  the  tartrate  of  anti- 
mony and  potash.     As  examples,  I  mention  mica,  called 
isinglass  by  the  common  people,  which  is  composed  of 
silica,  alumina,  oxyd  of  iron,  fluoric  acid,  and  water ;  and 
that  splendid  mineral,  so  much  used  for  making  costly 
vases  and  other  ornamental  articles,  lapis-lazuli,  which  is 
composed  of  silica,  alumina,  soda,  lime,  iron,  sulphuric 
acid,  sulphur,  chlorine,  and  water. 

11.  Mixtures  of  Compounds  in  the  Rocks. — In  many 
of  the  rocks  there  are  mixtures  of  the  mineral  compounds. 


14  MINERALOGY. 

Granite  is  in  contrast  with  marble  in  this  respect.  While 
the  latter  is  composed  of  one  compound  mineral,  the 
carbonate  of  lime,  the  former  has  mingled  together  in  a 
confused  manner  three  compounds — mica,  feldspar,  and 
quartz.  The  eye  can  generally  distinguish  readily  the 
three  kinds  of  crystals  imperfectly  formed.  A  full  con- 
sideration of  the  composition  of  the  rocks  will  claim  our 
attention  in  another  chapter. 

12.  Mineralogy,  Geology,  and  Chemistry. — While  Min- 
eralogy has  an  intimate  relation  with  Chemistry,  it  dif- 
fers from  it.  It  gets  from  Chemistry  the  composition  of 
the  various  minerals  of  which  it  treats,  but  it  has  noth- 
ing to  do,  as  Chemistry  has,  with  what  can  be  made  out 
of  these  substances,  or  what  can  be  extracted  from  them. 
It  treats  of  substances  simply  as  they  are  found  in  na- 
ture, without  regard  to  any  action  that  might  be  induced 
by  mingling  them  together.  Mineralogy  is  preparatory 
to  Geology,  because  it  gives  us  a  knowledge  of  the  min- 
eral substances  which  make  up  the  rocks.  The  three 
sciences  are  thus,  as  you  see,  linked  together,  and  the 
proper  order  for  their  study  is  that  which  I  have  adopted. 


CHAPTER  II. 

CONSTRUCTION    OF   MINERALS. 

13.  Crystallization. — When  a  mineral  substance  takes 
on  a  solid  form,  the  atoms  or  particles  are  disposed  to  an 
arrangement  which  is  termed  crystallization.  It  is  a 
very  definite  and  exact  arrangement,  with  straight  lines, 
perfect  angles,  and  plane,  smooth  faces.  Crystals  of 
quartz,  commonly  called  rock  crystal,  are  familiar  exam- 
ples. Mica  is  another  of  quite  a  different  kind,  the  crys- 
tals being  foliated — that  is,  in  leaves.  When  the  proc- 
ess of  forming  the  crystal  is  not  interfered  with  by  any 
circumstance,  as,  for  example,  agitation,  all  parts  of  it 


CONSTRUCTION    OF    MINERALS. 


15 


are  perfect.     The  crystal  of  alum,  for  in- 
stance, is   a  perfect  double  pyramid,  the 
shape  being  given  in  Fig.  1,  which  is  an 
octahedron  —  that  is,  a  body  with  eight 
equilateral  angles,  the  lines  all  being  ex- 
actly equal,  and  the  spaces  also.    The  name 
Fig.  i.         js  from  two  Greek  words,  octo,  eight,  and 
hedra,  base.     In  Fig.  2  you  have  the  crystals  of  alum  as 


Fig.  2. 


they  appear  when  their  formation  is  interfered  with  by 
some  disturbing  cause.  In  the  glistening  white  marble 
the  crystals  are  so  crowded  together  as  they  form  that 
none  of  them  are  perfect.  The  same  is  true  of  the  crys- 
tals of  quartz,  mica,  and  feldspar  in  granite. 

14.  Crystals  of  Different  Sizes. — As  crystals  increase 
by  additions  upon  the  outside,  the  crystals  of  any  sub- 
stance may  vary  greatly  in  size.  Quartz  crystals  are 
sometimes  very  large.  There  is  one  at  Milan  which  is 
3^  feet  long,  5-J  in  circumference,  and  weighs  870  pounds. 
Of  course,  the  larger  crystals  of  any  substance  will  have 
precisely  the  same  shape  with  the  smaller. 


16  MINERALOGY. 

15.  Crystallization  and  Vital  Growth  Contrasted. — 
While  crystallization  adds  to  the  outside  alone,  in  living- 
growth  there  is  addition  made  to  every  part  of  the  sub- 
stance.    The  additions  in  the  case  of  the  crystal  are  in- 
variably the  same,  and  all  parts  of  it  are  alike ;  but  a 
living  growth,  whether  vegetable  or  animal,  commonly 
differs  much  in  its  different  parts.    A  finger  and  a  quartz 
crystal,  for  example,  differ  widely  in  this  respect.     Far- 
ther: while  crystallization  tends  to  straight  lines  and 
exact  angles,  the  growth  of  animal  and  vegetable  sub- 
stances tends  to  curved  lines,  and  its  angles,  when  it 
makes  any,  are  not  sharply  defined.     The  branches  of 
trees  are  more  or  less  rounded,  and,  while  they  have  a 
general  angulai1  arrangement  with  the  trunk  of  the  tree, 
the  angles  are  not  definite. 

16.  Exceptions. — While  what  I  have  said  of  crystalli- 
zation is  generally  true,  there  are  some  exceptions.    The 

faces  of  diamonds  are  commonly  con- 
vex instead  of  plane,  and  the  edges 
are  therefore  curved.  In  Fig.  3  you 
have  the  usual  form  of  spathic  iron 
(carbonate  of  iron)  and*  pearl  spar 
(magnesian  carbonate  of  lime).  There 
is  sometimes  seen  in  limestone,  in 
clay-stones,  and  in  some  other  rocks, 
a  disposition  to  gather  in  spherical  forms,  and  the  proc- 
ess is  at  least  akin  to  crystallization.  The  arrangements 
of  crystals  are  very  often  in  beautiful  and  varied  imita- 
tion of  branches,  leaves,  and  flowers.  This  is  very  fa- 
miliar to  us  in  the  frostings  on  our  windows.  This  is 
seen  in  other  minerals,  as  in  alabaster  in  the  Mammoth 
Cave  of  Kentucky,  where  leaves,  vines,  and  flowers  are 
imitated,  some  of  the  "  rosettes"  being,  as  stated  by  Pro- 
fessor Dana,  a  foot  in  diameter.  In  all  such  cases  the 
curvings  are  in  the  arrangements  of  the  crystals,  each  in- 
dividual crystal  probably  being  in  its  usual  form. 

17.  Mineral  Matter  in  Living  Substances.— This  sub- 


.3ITT 


CONSTRUCTION 

ject  has  been  already  spoken  of  in  §  7.  1  introduce  it 
again  here  to  notice  the  fact  that  the  mineral  matter  is 
never  deposited  in  living  substances  in  any  thing  like  a 
crystalline  form.  Though  there  is  much  silica  (quartz) 
in  the  rushes,  there  are  no  quartz  crystals ;  and  the  phos- 
phate of  lime  in  bones,  though  its  particles  are  deposited 
after  a  certain  definite  plan  (as  seen  in  Fig.  84  in  my 
"Human  Physiology"),  exhibits  no  resemblance  to  the 
crystals  of  this  mineral. 

18.  Crystallization  not  Confined  to  Minerals. — Though 
organized  substances,  vegetable  or  animal,  never  take  on 
a  crystalline  form,  yet  some  of  the  products  contained 
within  them  may  do  so.    JThis  is  the  case  with  the  sugar 
of  the  sugar-cane  and  other  plants.     The  "  candying" 

of  raisins  is  an  example  of  the  crystalli- 
zation of  sugar.  The  crystals  which 
sugar  is  disposed  to  form  are  of  the 
shape  seen  in  I?ig.  4,  a  six-sided  prism, 
as  you  may  observe  in  what  is  called 
rig.  4.  rock-candy.  In  the  form  of  loaf  sugar 

the  crystals  are  huddled  together,  and  are  therefore  im- 
perfect, just  as  in  the  case  of  marble.  Many  of  the  veg- 
etable alkaloids,  morphine,  caffein,  etc.  (§  590,  Part  II.), 
are  obtained  in  the  crystalline  form.  In  all  these  cases 
the  crystals  are  never  formed  so  long  as  the  substance 
remains  under  the  influence  of  the  living  agency.  Sug- 
ar, for  example,  never  crystallizes  in  the  living  plant,  but 
only  after  it  is  taken  from  it. 

19.  Modes  of  Crystallization. — There  are  various  modes 
in  which  crystallization  occurs.    1.  One  of  the  most  com- 
mon modes  is  by  deposit  from  a  solution.     Thus  alum, 
salt,  sugar,  etc.,  may  form  crystals  from  a  solution,  the 
water  passing  off  by  evaporation.     When  the  substance 
can  be  dissolved  in  larger  amount  by  hot  water  than  by 
cold,  as  is  the  casje  with  alum,  but  not  with  salt,  consid- 
erable crystallization  can  be  obtained  before  evaporation 
begins  by  introducing  into  hot  water  as  much  of  the 


18  MINERALOGY. 

substance  as  it  can  take  up,  and  then  allowing  the  solu- 
tion to  cool.  The  formation  of  frost  is  really  crystalliza- 
tion by  deposition  from  a  solution,  for  the  water  depos- 
ited in  solid  form  was  dissolved  in  the  air  (§  96,  Part 
II.).  Warm  air  will  hold  more  water  in  solution  than 
cold,  and,  therefore,  when  warm  air  becomes  cooled,  it 
deposits  some  of  its  water  in  the  shape  of  dew  when  the 
cold  is  moderate,  and  in  the  solid  form  when  it  is  severe. 
2.  A  liquid  or  a  gas  may  be  converted  into  a  solid  with 
a  crystalline  arrangement.  Various  examples  of  this 
are  familiar  to  you,  as  the  formation  of  ice  from  water, 
the  freezing  of  mercury,  and  the  solidification  of  melted 
metals  on  cooling.  The  mosfc  common  example  which 
we  have  of  the  conversion  of  a  gas  or  vapor  into  a  crys- 
talline solid  is  in  the  formation  of  frost  from  the  vapor 
of  water  in  the  air.  3.  A  mineral  substance  which  is 
not  crystallized  may  become  so  by  heat,  and  perhaps 
some  other  agencies  acting  in  connection  with  this. 
Many  rocks,  as  you  will  see  illustrated  in  another  part 
of  this  book,  owe  their  crystalline  character  to  this  cause. 
It  is  in  this  way  that  marble  has  been  made  out  of  com- 
mon chalk  or  limestone,  it  differing  from  them  not  in 
chemical  composition,  but  merely  in  being  crystalline. 

20.  Water  of  Crystallization. — The  crystals  of  many 
minerals  have  water  incorporated  with  them,  and,  as  its 
presence  is  essential  to  their  crystalline  condition,  it  is 
termed  their  water  of  crystallization.     For  a  more  full 
statement  in  regard  to  this,  I  refer  you  to  §  164,  Part  II. 

21.  Amorphous  and  Dimorphous  Minerals. — A  mineral 
is  said  to  be  amorphous  when  it  is  destitute  of  all  trace 
of  crystalline  form.     The  term  comes  from  two  Greek 
words,  a,  without,  and  morphe,  form.     When  a  mineral 
appears  in  crystals  of  two  forms,  sometimes  the  one  and 
sometimes  the  other,  it  is  said  to  be  dimorphous,  the  first 
part  of  the  term  coming  from  the  Greek  word  dis,  twice. 

22.  Arrangements  of  Crystals.  —  Crystals  forming  in 
groups  are  arranged  variously  by  the  influence  of  cir- 


CONSTRUCTION    OF   MINERALS. 


19 


cumstances.  This  is  exemplified  in  the  huddling  togeth- 
er of  imperfectly  formed  crystals  in 
marble,  loaf  sugar,  etc.,  and  in  the 
extremely  varied  forms  of  frost-work 
and  other  similar  crystallizations  (§ 
16).  Some  crystals  are  arranged  in 
the  form  of  a  cross,  as  seen  in  Fig.  5. 
Sometimes  two  similar  crystals  are 
united  together,  and  then  we  are  said 
to  have  a  twin  crystal.  The  crys- 


Fig.  5. 


tals  of  common  salt  are  apt  to  as- 

sume the  hopper  arrangement  rep- 

resented in  Fig.  6.     This  is  because 

that,  as  the  evaporation  takes  place, 

the  gravity  of  the  salt  makes  the 

mass  sink  constantly  a  little  below 

the  surface,  and  each  set  of  crystals 

is  deposited  on  the  upper  and  outer  edge  of  the  preced- 

ing set. 

23.  Regularity  of  Form  in  Rocks. — We   have   some- 
thing akin  to  crystallization  in  a  rude  way  in  the  gen- 
eral lines  and  faces  of  rocks.     We  have  the  laminated 
arrangement  in  the  slate  rocks,  and  the  magnificent  co- 
lumnar arrangement  in  the  trap  rocks,  as  exemplified  in 
the  Giant's  Causeway.     Then  there  are  joints,  so  called, 
running  across  strata  or  layers  of  rock,  and  dividing 
them  sometimes  as  evenly  as  if  it  were  done  with  a 
knife.     All  this  will  be  fully  illustrated  in  the  geological 
portion  of  this  book. 

24.  Cleavage. — Some  minerals  can  have  layers  chip- 
ped or  cleaved  off,  leaving  as  smooth  surfaces  as  before. 
Mica  is  a  very  familiar  example  of  cleavage  from  planes. 

Sometimes  the  cleavage  can 
be  made  from  angles,  as 
seen  in  Fig.  V,  and  some- 
times from  edges,  as  seen  in 
Fig.  8.  The  planes  made 
Fig.  i.  Fig.s.  by  cleaving  a  crystal  are 


20 


MINERALOGY. 


called  its  cleavage  planes.  Minerals  sometimes  cleave 
in  only  one  direction,  as  common  mica  and  foliated  gyp- 
sum, and  sometimes  in  two,  three,  or  four  directions. 
In  many  minerals  it  is  difficult  to  effect  cleavage ;  in 
some,  as  quartz,  it  is  impossible,  though  even  in  this  case 
it  has  been  done  by  heating  the  crystal,  and  then  plung- 
ing it  into  cold  water. 

25.  Primary  Forms. — While  there  is  vast  variety  in 
the  forms  of  crystals  as  found  in  nature,  mineralogists 
have  discovered  by  cleavage  that  the  primary  or  funda- 
mental forms  are  few  in  number.  There  are  only  thir- 
teen of  these  forms,  which  are  the  solids  that  have  been 
obtained  from  the  various  minerals  by  cleavage.  These 
are  divided  into  six  classes,  each  class  containing  those 
which  can  be  produced  by  cleavage  from  each  other. 
The  first  contains  the  three  solids  represented  in  Figs.  9, 


Fig.  9.  Fig.  10.  Fig.  11. 

10,  and  11,  the  cube  having  four  equal  square  sides,  the 
octahedron  having  for  sides  eight  equilateral  triangles, 
and  the  rhombic  dodecahedron,  whose  twelve  sides  are 
equal  rhombic  planes.*  I  will  show  by  figures  how  the 

*  The  name  dodecahedron  is  from  the  Greek  words  dodeka,  twelve, 
and  hedra,  base.  A  rhombic  plane,  or  rhomb,  is  a  plane  with  four 
equal  sides,  those  which  are  opposite  being  parallel,  and  the  angles 
being  unequal,  two  of  them  being  acute  and  two  obtuse.  It  differs 
from  a  square  in  being  oblique-angled  instead  of  right-angled.  You 

see  the  difference  in  the  two  fig- 
ures. The  angles  of  the  square 
are  all  equal,  but  in  the  rhomb  a 
and  its  opposite  angle  are  equal, 
being  obtuse,  and  b  and  its  oppo- 
site angle  are  equal,  being  acute. 


CONSTRUCTION    OF   MINERALS. 


21 


cube  and  the  octahedron  can  be  converted  into  each  oth- 
er by  cleavage.  If  the  cube  have  its  angles  cleaved  as 
indicated  by  the  dotted  lines  in  Fig.  12,  you  have  as  a 


Fig.  1-2. 


Fig.  13. 


Fig.  14. 


result  the  body  represented  by  Fig.  13.  If  you  continue 
the  process,  you  will  at  length  obtain  the  solid  represent- 
ed in  the  middle  of  Fig.  14 — that  is,  the  octahedron.  If, 
on  the  other  hand,  you  take  an  octahe- 
dron, and  cleave  it  as  represented  in  Fig. 
1 5,  you  will  at  length  obtain  the  cube  as 
indicated.  These  processes,  and  other 
similar  ones  in  regard  to  other  forms, 
may  be  gone  through  with  very  satisfac- 
torily with  raw  potatoes  and  a  common 
knife. 

26.  Secondary  Forms. — If  with  a  knife  you  make  such 
cleavages  as  are  represented  in  Fig.  8,  you  produce  a 
secondary  form.  Now,  in  nature,  this  result  is  not  pro- 
duced by  cleavage,  but  by  an  omission  to  fill  out  the 
whole  figure,  the  omission  falling  short  in  various  de- 
grees in  different  cases.  The  omission  may  occur  on  the 
angles  instead  of  the  edges,  as  seen  in  Fig.  7. 

Instead  of  omission  there  may  be  addi- 
tion, as  represented  in  Fig.  16.  Here,  by 
an  addition  in  the  shape  of  a  low  pyramid 
to  each  side  of  a  cube,  the  dodecahedron  is 
produced.  The  addition  on  one  of  the  faces 
of  the  cube  is  shaded  to  make  it  obvious. 
The  increase  is  by  layer  upon  layer  of  particles,  each 
layer  having  a  less  number  of  particles  than  the  pre- 
ceding one.  This  is  indicated,  in  a  coarse  way,  by 


Fig.  16. 


22  MINERALOGY. 

Fig.  1 7,  the  particles  or  molecules  being 
in  reality  so  minute  that  no  inequality 
is  perceptible  to  the  eye  on  the  surface 
of  the  crystal. 

27.  Constancy  in  the  Forms  of  Crys- 
tals.—  Notwithstanding   the   immense 
Fig.  17.  variety  in  the  secondary  forms  of  crys- 

tals, there  is,  in  the  case  of  each  mineral,  a  strict  adher- 
ence to  its  own  form  or  forms  in  all  essential  character- 
istics. The  size  and  number  of  faces  may  differ  in  dif- 
ferent specimens  so  much  as  to  give  them  an  entirely 
different  appearance,  but  the  mineralogist  will  discover 
their  relation  to  each  other  by  observing  that  the  corre- 
sponding angles  are  exactly  the  same,  and  by  cleavage 
he  will  find  the  same  fundamental  form.  "  Crystals  are, 
therefore,"  says  Professor  Dana,  "the  perfect  individuals 
of  the  mineral  kingdom.  The  mineral  quartz  has  a  spe- 
cific form  and  structure,  as  much  as  a  dog  or  an  elm, 
and  is  as  distinct  and  unvarying  as  regards  essential  char- 
acters, although,  owing  to  counteracting  causes  during 
formation,  these  forms  are  not  always  assumed.  In 
whatever  part  of  the  world  crystals  of  quartz  may  be 
obtained,  they  are  fundamentally  identical." 

28.  Symmetry. — In  all  the  modifications  of  crystals 
seen  in  the  production  of  secondary  forms  there  is  a 
wonderful  symmetry.  If  one  part  is  modified,  all  the 
corresponding  parts  are  modified,  and  in  the  same  way, 
either  over  the  whole  crystal  or  over  just  one  half  of  it. 
Thus,  if  we  find  a  plane  in  place  of  an  edge,  we  shall  find 
the  other  edges  also  replaced  by  planes  of  precisely  the 
same  width,  as  seen  in  Fig.  8  ;  and  so  of  the  angles 
also,  as  represented  in  Fig.  7.  So,  if  there  be  two  planes 
in  place  of  any  edge  or  angle,  there  will  be  found  the 
same  planes  replacing  the  other  edges  or  angles ;  and 
the  same  is  true  if  there  be  many  replacing  planes,  as 
there  often  are.  You  see  how  this  secures  a  regularity 
pleasing  to  the  eye  in  the  midst  of  extreme  variety,  thus 


CAEBON   AND   ITS    COMPOUNDS.  23 

adding  largely  to  the  beauty  of  the  mineral  world.  Ob- 
serve that  there  is  here  some  analogy  to  the  symmetry 
that  appears  in  living  forms.  The  two  halves  of  a  face, 
for  example,  are  generally  exactly  alike,  just  as  are  the 
corresponding  parts  of  a  crystal.  What  the  agency  is 
that  produces  the  result  is  in  both  cases  a  wonderful 
mystery.  All  that  we  know  is  that  in  the  one  case  the 
deposition  of  matter  is  guided  unerringly  by  a  living 
agency,  and  in  the  other  by  one  that  is  not  living. 


CHAPTER  III. 

CAEBON  AND   ITS   COMPOUNDS. 

I  PEOCEED  now  to  treat  of  different  kinds  of  minerals, 
grouping  them  according  to  their  natural  affinities. 

29.  Diffusion  of  Carbon. — As  carbon  is  one  of  the  four 
grand  elements  in  the  composition  of  vegetable  and  ani- 
mal substances,  there  is  a  constant  interchange  in  regard 
to  it  between  the  vegetable,  animal,  and  mineral  worlds, 
and  therefore  it  is  widely  diffused,  and  appears  in  vari- 
ous combinations.     Combined  with  oxygen,  it  exists  ev- 
ery where  in  the  atmosphere  in  •the  form  of  carbonic 
acid,  which  is  one  of  the  gases  that  are  more  or  less  min- 
gled or  dissolved  in  the  water  of  the  earth.     The  car- 
bonates are  important  salts,  the  most  important  being 
the  carbonate  of  lime,  which  appears  in  the  various  forms 
of  chalk,  limestone,  and  marble,  and  in  the  animal  world 
makes  the  hard  covering  of  shell-fishes  and  the  skeletons 
of  the  coral  animals.     The  immense  stores  of  coal  laid 
up  in  the  bowels  of  the  earth  is  almost  wholly  carbon. 

30.  The  Diamond. — In  strong  contrast  with  the  im- 
mense provision  of  carbon  in  the  form  of  coal,  this  ele- 
ment is  laid  up  here  and  there  in  very  small  quantities, 
equally  for  the  use  of  man,  in  the  most  costly  and  splen- 
did of  gems.     That  the  diamond  is  pure  carbon  is  proved 


24  MINERALOGY. 

by  burning  it  in  oxygen  gas,  the  product  being  carbonic 
acid  gas,  a  compound  of  carbon  and  oxygen,  just  as  in 
the  burning  of  charcoal.  As  in  pure  charcoal  and  an- 
thracite we  have  carbon  alone,  the  diamond  differs  from 
them  merely  in  the  arrangement  of  the  atoms.  It  is  this 
alone  that  causes  the  immense  difference  in  characteris- 
tics. When  the  diamond  is  colored,  as  it  sometimes  is, 
there  is  coloring  matter  intimately  mingled  with  the  car- 
bon, as  glass  is  colored  with  something  added  to  it.  But 
the  quantity  of  coloring  matter  is  so  exceedingly  minute 
that  it  could  not  be  detected  unless  a  considerable  amount 
of  diamond  were  burned,  an  experiment  so  expensive  that 
I  presume  that  it  never  has  been  tried. 

31.  Qualities  of  the  Diamond. — It  is  the  hardest  of  all 
substances.     Its  lustre  is  peculiar ;  and  other  gems  that 
are  similar  to  it  in  this  respect  are  said  to  have  an  ada- 
mantine lustre.     Its  reflection  of  light  is  exceedingly 
brilliant.     It  is  commonly  colorless,  but  sometimes  red, 
yellowish,  orange,  green,  or  black.     The  rose  diamond  is 
highly  valued  for  the  beauty  of  its  color,  and  so  also  is 
the  green  diamond.     The  black  diamond  is  very  rare, 
and  therefore  commands  a  high  price,  although  it  has  no 
beauty. 

32.  Size  of  Diamonds. — In  speaking  of  the  size  of  dia- 
monds the  term  carat  is  used.     This  is  the  name  of  a 
bean,  which  was  used  in  its  dried  state  by  the  natives  of 
Africa  in  weighing  gold,  and  in  India  in  weighing  dia- 
monds.   Though  the  bean  is  not  used  for  this  purpose 
now,  the  name  is  retained,  and  the  carat  is  nearly  four 
grains  Troy.     The  largest  diamond  known  is  in  the  pos- 
session of  the  Great  Mogul.     It  weighed  originally  900 
carats,  or  2769  grains,  but  it  was  reduced  by  cutting  to 
861  grains.     It  is  of  the  size  of  half  a  hen's  egg,  and  is  in 
that  form.     The  Pitt  or  Regent  diamond  weighs  419 
grains.     The  famous  Koh-i-noor  weighed  originally  186 
carats,  but  was  reduced  by  recutting  one  third. 

33.  Cost  of  Diamonds.— The  cost  of  diamonds  depends 


CARBON   AND   ITS    COMPOUNDS.  25 

upon  the  weight,  the  purity,  and  the  color.  A  diamond 
which,  after  being  cut,  weighs  one  carat,  is  worth  com- 
monly £8.  The  price  increases  largely  with  the  size,  for 
one  weighing  four  carats  would  be  worth  £128,  and  one 
often  carats  would  be  £800.  When  we  get  Tip  to  twenty 
carats  the  prices  rise  much  more  rapidly.  The  Regent 
diamond  is  estimated  at  £125,000. 

34.  Cutting  of  Diamonds. — The  art  of  cutting  and  pol- 
ishing diamonds  was  unknown  till  1456,  when  it  was  dis- 
covered by  Louis  Berquen,  of  Bruges.     The  process  is 
thus  described  by  Professor  Dana.     "  The  diamond  is  cut 
by  taking  advantage  of  its  cleavage,  and  also  by  abrasion 
with  its  own  powder,  and  by  friction  with  another  dia- 
mond.    The  flaws  are  first  removed  by  cleaving  it,  or 
else  by  sawing  it  with  an  iron  wire,  which  is  covered 
with  diamond  powder — a  tedious  process,  as  the  wire  is 
generally  cut  through  after  drawing  it  across  five  or  six 
times.     After  the  portion  containing  flaws  has  thus  been 
cut  off,  the  crystal  is  fixed  to  the  end  of  a  stick,  in  a 
strong  cement,  leaving  the  part  projecting  which  is  to  be 
cut;  and  another  being  prepared  in  the  same  manner, 
the  two  are  rubbed  together  till  a  facet  is  produced.    By 
changing  the  position,  other  facets  are  added  in  succes- 
sion till  the  required  form  is  obtained.     A  circular  plate 
of  soft  iron  is  then  charged  with  the  powder  produced 
by  the  abrasion,  and  this,  by  its  revolution,  finally  polish- 
es the  stone.     To  complete  a  single  facet  often  requires 
several  hours."    The  expense  of  cutting  the  Regent  dia- 
mond was  estimated  at  £5000  sterling,  and  the  mere  fil- 
ings at  £7000  sterling. 

35.  Uses  of  the  Diamond. — The  most  familiar  use  of 
the  diamond  is  cutting  glass.     It  is  also  used  for  lenses 
in  microscopes.     Diamonds  that  can  not  be  worked  are 
sold  under  the  name  of  bort^  for  various  uses.     Splinters 
of  bort  are  made  into  fine  drills  for  drilling  artificial 
teeth  and  gems  of  various  kinds. 

36.  Localities  of  Diamonds. — Diamonds  are  found  in 

B 


26  MINERALOGY. 

various  parts  of  India  and  of  Brazil,  in  Africa,  in  the  isl- 
and of  Borneo,  and  in  the  Urals  of  Russia.  The  original 
rock  of  the  diamond  appears  to  be  a  quartz  rock;  but  the 
diamonds  are  almost  always  obtained  from  amid  the 
sands  and  $e*bbles  which  have  come  from  the  rocks,  and 
are  scattered  in  the  rivers  and  brooks.  In  Brazil,  collec- 
tions are  made  of  these  sands  and  pebbles,  and  by  wash- 
ing them  in  a  series  of  boxes  the  diamonds  are  discovered 
and  gathered.  If  a  negro  be  so  fortunate  as  to  find  a 
diamond  weighing  1 7 \  carats,  he  gains  a  boon  which  is 
above  the  price  of  gems — the  boon  of  liberty. 

37.  Graphite. — Graphite,  or  Plumbago,  commonly  call- 
ed black  lead,  although  there  is  not  a  particle  of  lead  in 
it,  is  composed  of  carbon,  with  a  small  proportion  of  iron, 
commonly  to  the  amount  of  from  4  to  10  per  cent.    Some 
have  supposed  it  to  be  a  carburet  of  iron  ;  but  it  is  not  a 
chemical  compound.     It  is  only  a  mixture  of  the  carbon 
and  iron,  and  that  the  iron  is  not  essential  is  shown  by 
the  fact  that  in  some  cases  there  is  scarcely  a  trace  of  it. 
Graphite  is  soft,  and  has  a  shining  lustre.     It  is  some- 
times compact,  and  sometimes  crystalline,  usually  in  the 
foliated  form,  but  occasionally  in  six-sided  prisms.     It  is 
used  in  making  lead-pencils,  in  lessening  the  friction  of 
machinery,  in  giving  a  gloss  to  stoves,  etc.     Commonly, 
in  preparing  graphite  for  pencils,  the  solid  mineral  is  cut 
up  into  pieces  of  the  requisite  size ;  but  a  method  has  of 
late  been  adopted  by  which  the  mineral  is  finely  pow- 
dered, and  then,  by  great  pressure,  made  into  solid  sheets, 
from  which  the  pieces  are  obtained. 

38.  Coal. — The  varieties  of  coal  are  divided  into  two 
classes,  the  bituminous  and  the  non-bituminous.    The 
former  have,  in  addition  to  the  carbon,  hydrogen,  which 
in  the   combination  produces  carbureted  hydrogen,  or 
common  illuminating  gas,  and  it  is  the  burning  of  this, 
that  is,  its  union  with  the  oxygen  gas  of  the  air,  that 
causes  the  flame.     In  the  non-bituminous,  the  anthracite, 
on  the  other  hand,  we  have  only  the  blue  flame  in  the 


CARBON   AND   ITS   COMPOUNDS.  27 

beginning  of  its  combustion,  which  comes  from  the  car- 
bonic oxyd  gas  as  it  unites  with  the  oxygen  of  the  air  to 
form  carbonic  acid.  The  formation  of  this  gas  in  the  an- 
thracite fire  is  fully  explained  in  §  67,  Part  II.  It  is  from 
the  bituminous  coal  that  the  illuminating  gSfcs  produced, 
there  being  no  hydrogen  in  the  anthracite  for  its  forma- 
tion. The  explanation  of  the  process  is  this:  By  the  ap- 
plication of  heat  the  hydrogen  is  driven  off,  and  it  takes 
with  it  enough  of  the  carbon  to  make  it  carbureted  hy- 
drogen ;  but  most  of  the  carbon  is  left  behind  in  a  light, 
porous  condition,  to  which  is  given  the  name  of  coke. 

39.  Anthracite. — This  is  the  common  name  given  to 
coal  which  is  either  mostly  or  wholly  free  from  bitumen. 
It  is  supposed  that  it  was  subjected  to  more  heat  than 
the  bituminous  was  after  its  formation,  by  which  the  bi- 
tuminous elements  were  driven  off.    The  coke,  which  is 
left  after  the  making  of  illuminating  gas,  is  very  much 
the  same  thing  as  anthracite,  except  that,  as  it  has  not 
been  subjected  to  great  pressure,  it  has  not  the  same 
closeness  of  structure.    Anthracite  is  hard,  and  so  is  often 
called  very  appropriately  stone  coal.     From  80  to  90  per 
cent,  of  it  is  carbon.     Then  there  is  from  4  to  7  per  cent, 
of  water,  and  there  are  some  impurities,  as  silica,  alumi- 
na, lime,  magnesia,  etc.     The  redness  of  the  ash  of  some 
kinds  of  coal  comes  from  the  presence  of  oxyd  of  iron. 
The  slag^  or  glassy  substance  which  you  find  in  the  refuse 
of  the  combustion,  is  composed  of  silicates.     These  do 
not  form  with  the  ordinary  burning  of  coal  in  grates,  be- 
cause the  heat  is  not  intense  enough.     The  clinker  which 
collects  on  the  inside  of  stoves  is  slag.    The  reason  that 
oyster-shells  put  into  the  fire  clear  off  the  clinker  is  that 
the  lime  makes  the  silicates  more  fusible,  and  so  dislodges 
the  clinker,  mingling  it  with  the  burning  coal.     Anthra- 
cite has  a  fine  lustre,  and  often  an  iridescent  play  of  col- 
ors.   It  is  capable  of  a  high  polish,  and  has  sometimes 
been  made  into  inkstands  and  other  articles. 

40.  Bituminous  Coal. — This  is  softer  than  anthracite, 


28 


MINERALOGY. 


and  has  less  lustre.  Its  chief  varieties  are  the  pitching 
or  caking  coal,  which  in  burning  is  apt  to  cake  or  unite 
into  solid  masses,  and  the  cannel  coal,  which  burns  with 
so  clear  a  flame  that  it  has  sometimes  been  used  as  can- 
dles. Inkstslros,  boxes,  etc.,  are  made  from  it.  The  min- 
eral called  jet,  so  much  used  in  jewelry,  is  allied  to  can- 
nel coal,  but  has  a  much  deeper  color,  and  is  capable  of 
a  brilliant  polish.  Brown  coal,  or  lignite,  is  not  so  per- 
fectly formed  coal  as  the  other  varieties,  and  the  struc- 
ture of  the  original  wood  is  often  apparent  in  it. 

41.  Coal  of  Vegetable  Origin. — That  coal  is  made  from 
plants  might  be  properly  inferred  from  the  remains  and 
impressions  of  the  plants  found  in  the  layers  of  rocks  be- 
tween which  the  coal  is  packed,  and  sometimes  found 
even  in  the  coal  itself.  But  the  proof  is  more  positive 
than  this.  Vegetable  structure  is  found  in  the  coal  by 
microscopical  examination.  A  piece  of  anthracite  coal 
which  has  been  partially  burnt  is  used,  because  the  vege- 
table cells,  being  somewhat  silicious,  remain  unaltered 

in  the  burning  out 
Of  a  p0rtion  of  the 
carbon.  In  Fig.  1 8, 
«,  we  have  repre- 
sented a  small  bit 
of  such  a  piece  of 
anthracite  as  seen 
through  the  micro- 
scope. The  ducts 
lie  side  by  side,  as 
they  did  ages  ago 
in  the  woody  fibre 
of  the  plant.  In  b 
two  of  the  ducts  are 
very  highly  magnified,  the  white  spaces  showing  us  the 
silica,  and  the  black  lines  the  carbon  which  was  not 
burned  out.  The  evidence  from  such  an  examination  is 
not  as  clear  in  soft  bituminous  coal,  because  the  original 
texture  is  not  so  well  preserved. 


Fig.  18. 


CARBON   AND    ITS   COMPOUNDS.  29 

42.  Why  Coal  is  called  a  Mineral. — Coal  being  thus  of 
vegetable  origin,  and  retaining  the  evidences  of  this  in 
its  very  texture,  it  might  at  first  thought  appear  that  it 
could  hardly  be  called  a  mineral.     The  reason  that  it  is 
proper  to  call  it  so  I  will  point  out.     Thenoarbon,  which 
is  the  chief  component  of  all  kinds  of  coal — almost  the 
only  component  of  one  kind,  the  anthracite — does  not  ex- 
ist in  the  vegetable  as  carbon,  but,  chemically  united  with 
oxygen  and  hydrogen,  it  forms  woody  fibre.     It  is  just 
as  sulphur  does  not  exist  as  sulphur  in  sulphate  of  lime 
(gypsum),  but  as  a  part  of  a  compound  united  chemical- 
ly in  it  with  oxygen  and  lime,  as  carbon  in  wood  is  united 
chemically  with  oxygen  and  hydrogen.    Now  when  wood 
is  made  to  produce  coal  a  chemical  change  occurs,  a  real 
decomposition  is  effected,  so  that  carbon  now  appears  in 
its  uncombined  state.     The  form,  indeed,  of  woody  fibre 
may  remain,  but  it  is  no  longer  wood — the  compound  of 
carbon,  oxygen,  and  hydrogen.     These  elements  are  sep- 
arated from  each  other;  and  if  they  are  combined,  as  may 
be  the  case  in  bituminous  coal,  it  is  a  recombination  after 
separation.    A  farther  chemical  change  or  decomposition 
is  produced  when  the  coal  is  burned,  all  the  carbon  then 
passing  off  by  forming  carbonic  acid  gas  with  the  oxy- 
gen of  the  air.     The  first  process  is  as  strictly  and  fully  a 
chemical  change  as  the  last,  and  it  is  by  chemical  changes 
that  minerals  are  produced.     We  have  here  a  clear  case 
of  the  passage  of  an  organized  substance  under  the  con- 
trol of  living  agencies  over  into  the  mineral  kingdom, 
where  chemical  laws  bear  sway. 

43.  Peat. — In  peat  we  have  an  example  of  imperfect 
formation  of  coal,  the  approach  to  the  completion  of  the 
process  being  different  in  different  cases.     It  accumulates 
in  sivampy  places,  mostly  from  the  growth  of  mosses  of 
one  genus,  Sphagnum.     The  roots  continually  die  below 
as  the  plant  grows  upward ;  and  as  these  roots,  by  the 
partial  decomposition  under  water,  change  into  peat,  a 
bed  of  great  thickness  may  after  a  time  be  formed. 


30  MINERALOGY. 

There  is  sometimes  a  depth  of  forty  feet  in  a  peat-bed. 
The  beds  in  some  countries  are  very  extensive.  They 
cover  one  tenth  of  Ireland,  and  one  of  them  is  fifty  miles 
long  and  two  or  three  in  breadth.  It  is  estimated  that 
the  amount -of  peat  in  Massachusetts  is  120  millions  of 
cords. 

44.  Diffusion  of  Coal  in  the  Earth. — The  stores  of  coal 
in  the  earth  are  immense.     The  provision  which  has  been 
made  by  the  Creator  in  this  respect  for  the  wants  of  man, 
and  the  means  which  have  been  adopted  for  bringing  the 
coal  within  his  reach,  are  among  the  highest  evidences 
of  far-reaching  design  and  system  in  the  construction  of 
the  earth.     This  point,  barely  alluded  to  here,  will  be 
fully  developed  in  another  part  of  this  book. 

45.  Amber. — This  is  a  resin  from  some  tree  which  has 
been  chemically  changed,  or  mineralized,  as  it  is  express- 
ed.   It  is  found  in  lumps  of  various  sizes,  from  small  bits 
up  to  even  the  size  of  a  man's  head.    It  is  commonly  of 
a  yellowish  color,  has  considerable  lustre,  and  is  suscep- 
tible of  a  polish.    It  is  appropriated  to  ornamental  pur- 
poses, but  it  is  not  highly  prized  in  this  respect,  as  it  is 
soft,  yielding  readily  to  the  knife,  and,  besides,  can  be 
easily  counterfeited.     It  is  used  in  making  a  superior 
transparent  varnish.     There  are  sometimes  seen  in  speci- 
mens of  amber  insects  and  parts  of  insects,  which  became 
enveloped  in  the  resin  in  its  semi-liquid  state.    Such  spec- 
imens are  highly  prized,  because  it  is  supposed  these  in- 
sects lived  ages  before  the  creation  of  man.    Imitations, 
therefore,  have  sometimes  been  made,  and  have  been 
palmed  off  upon  those  who  are  not  able  to  distinguish 
insects  of  those  early  ages  from  the  insects  of  the  pres- 
ent day,*    Amber  becomes  electric  when  it  is  rubbed, 

• 

*  In  the  geological  part  of  this  book  you  will  learn  that  both  the 
animals  and  plants  of  the  early  ages  of  the  earth  differed,  in  some  re- 
spects, from  those  which  exist  at  the  present  time.  The  imposture 
referred  to  reminds  me  of  one  which  was  once  detected  in  the  court- 
room when  a  will  case  was  on  trial.  The  will,  on  being  held  up  to 


5IT7J 


CARBON   AND   ITS 

and  therefore  its  Greek  name  electron  gave  rise  to  the 
term  electricity. 

46.  Bitumen. — There  are  various  kinds  of  bitumen, 
some  solid  and  some  fluid.  They  are  supposed  to  be 
produced  from  vegetable  matters  buried  in  the  earth ; 
and  as  they  are  commonly  found  in  the  neighborhood  of 
active  or  extinct  volcanoes,  it  is  inferred  that  they  have 
been  driven  to  the  surface  by  the  internal  heat  of  the 
earth.  I  w^ll  notice  some  of  the  varieties.  Asphaltum, 
or  mineral  pitch,  is  solid.  It  was  the  chief  ingredient 
in  the  cement  used  in  building  the  walls  of  Babylon  and 
of  the  Temple  in  Jerusalem.  It  has  lately  been  success- 
fully employed  in  forming  a  composition  for  paving 
streets,  and  a  cement  for  covering  roofs.  It  is  very 
abundant  on  the  shores  of  the  Dead  Sea,  which  is  called 
Asphaltites  for  this  reason.  The  most  remarkable  local- 
ity of  it  is  the  Pitch  Lake  in  the  island  of  Trinidad.  It 
is  about  a  mile  and  a  half  in  circumference,  and  while 
the  asphaltum  is  near  the  shores  sufficiently  hard  at  most 
seasons  to  sustain  men  and  quadrupeds,  it  grows  soft  and 
warm  as  you  go  toward  the  centre,  and  there  it  is  in  a 
boiling  state.  Petroleum  is  a  dark  fluid,  which  becomes 
solid  on  exposure  to  the  air.  This  is  so  abundant  in  the 
Burmese  Empire  that  it  is  used  as  lamp-oil,  and  as  fuel, 
by  being  mixed  with  ashes  or  earth.  The  most  power- 
ful springs  of  it  there  are  on  the  Irawady.  In  one  local- 
ity there  are  520  wells,  yielding  annually  400,000  hogs- 
heads. There  are  many  localities  of  petroleum  in  this 
country.  It  was  formerly  collected  and  sold  by  the  In- 
dians ;  and,  as  the  Senecas  were  prominent  in  the  trade, 

the  light,  was  found  to  have  been  written  on  paper  which,  by  its  wa- 
ter-mark, was  shown  to  have  been  manufactured  subsequent  to  the 
date  of  the  document.  So,  in  these  imitations  of  amber,  the  date 
fixed  by  the  recent  character  of  the  insects  shows,  to  the  practiced  eye 
of  one  who  understands  the  distinctions  between  insects  of  the  present 
age  and  those  of  ages  previous  to  the  creation  of  man,  that  the  speci- 
mens are  not  real  amber. 


32  MINERALOGY. 

it  acquired  the  name  of  Seneca  oil,  which  it  still  retains. 
Naphtha  is  a  light,  limpid  fluid  of  a  yellowish  color,  and 
is  a  purer  article  than  petroleum,  from  which  it  can  be 
obtained  by  distillation.  It  is  a  hydrocarbon ;  that  is, 
it  is  composed  of  hydrogen  and  carbon.  As  there  is  no 
oxygen  in  its  composition,  it  is  used,  as  you  learned  in 
Part  II.,  by  the  chemist  to  preserve  potassium  and  so- 
dium in  their  metallic  state. 

47.  Carbonic  Acid. — The   qualities   of  thjs   gas  you 
learned  in  Part  II.,  Chap.  III.     It  is  constantly  furnished 
to  the  air  from  the  respiration  of  animals,  from  fires,  and 
from  the  decomposition  of  vegetable  and  animal  matters. 
As  it  is  constantly  absorbed  by  the  leaves  of  plants,  its 
undue   accumulation  in  the  atmosphere  is  prevented. 
There  are  localities  where  this  gas  is  produced  in  the 
earth  in  large  quantities.     In  some  mineral  springs,  as  at 
Saratoga,  it  gives  briskness  and  a  slight  pungent  taste  to 
the  waters.     This  large  production  of  it  appears  in  the 
neighborhood  of  some  volcanoes.     A  cavern  near  Na- 
ples, the  Grotto  del  Cane,  has  a  world-wide  reputation  on 
account  of  the  abundance  of  this  gas  in  it,  which  fills  the 
cavern  up  to  the  level  of  the  lower  margin  of  its  en- 
trance.    This  gas  has  a  great  agency  in  relation  to  one 
of  the  most  important  and  extensive  of  the  rocks  of  the 
earth,  the  limestone,  which  is  a  combination  of  this  gas 
with  lime.     The  carbonate  of  lime  of  the  rocks  is  contin- 
ually being  dissolved  in  the  water  that  comes  in  contact 
with  them ;  and  then  the  shell-fish  and  the  coral  animals 
appropriate  this  to  make  their  shells  and  skeletons,  which 
eventually  become,  as  you  have   seen  (§  8),  limestone 
rock,  thus  returning  the  carbonate  of  lime  to  the  source 
from  which  it  came.     Now  it  is  the  carbonic  acid  in  the 
water  which  enables  it  to  dissolve  sufficient  of  the  lime- 
stone to  supply  the  shell-fish  and  the  corals  with  this  ma- 
terial.    For  a  full  elucidation  of  this  interesting  point  I 
refer  you  to  Part  II.,  §  306. 

48.  Carbureted  Hydrogen. — This,  which  is  the  common 


SULPHUR   AND   ITS   COMPOUNDS. 


33 


illuminating  gas,  produced  from  bituminous  coal  artifi- 
cially, is  produced  naturally  in  many  localities,  and  prob- 
ably comes  from  the  action  of  heat  upon  bituminous 
coal,  or  some  other  substance  of  a  kindred  character.  In 
the  village  of  Fredonia,  New  York,  near  Lake  Erie,  this 
gas  issues  so  abundantly  from  a  slate  rock  that  it  is  col- 
lected, and  is  used  by  the  inhabitants  for  lighting  the 
place. 


CHAPTER  IV. 

SULPHUR   AND   ITS    COMPOUNDS. 

49.  Native  Sulphur. — This  substance  is  of  a 
pale  yellow  color.  It  is  found  both  crystallized 
and  uncrystallized.  Its  crystallized 
form  is  an  octahedron,  as  seen  in  Fig.  --N 
1 9.  When  sulphur  is  melted,  and  then 
left  to  crystallize,  the  crystal  takes  the 
form  seen  in  Fig.  20,  which  is  very  dif- 
Fig.  w.  ferent  from  the  forms  which  are  as- 
sumed in  nature.  Sulphur  is  often  found  in  fis- 
sures and  cavities  in  lava.  The  most  important 
locality  of  sulphur  is  Sicily.  Sixteen  or  seven- 
teen thousand  tons  are  imported  annually  into 
England  from  Sicily,  to  say  nothing  of  the  sup- 
ply to  other  countries.  Much  of  the  sulphur 
of  commerce  is  obtained  from  the  sulphurets  of  iron  and 
copper.  The  sulphur  is  driven  off  from  these  ores  by 
heat,  and  is  collected  in  brick  chambers.  It  is  one  of  the 
ingredients  of  gunpowder,  and  is  used  in  bleaching  and 
in  the  manufacture  of  sulphuric  acid,  as  described  in  § 
249,  Part  II. 

50.  Sulphurets  of  Iron. — The  bisulphuret  of  iron  is  one 
of  the  most  common  ores  in  the  earth,  and  has  been  known 
from  ancient  times,  when  it  received  the  name  of  pyrites, 
from  the  Greek  word  pur,  fire,  because,  as  Pliny  says, 

B2 


Fig.  20. 


34  MINEEALOGY. 

/ 

"  there  is  much  fire  in  it,"  referring  to  its  readily  strik- 
ing fire  with  steel.  It  occurs,  when  crystallized,  in  the 
primary  forms  of  cube,  octahedron,  and  dodecahedron 
(Figs.  9, 10,  and  11),  and  in  a  variety  of  secondary  forms. 
Its  color  is  a  bronze-yellow,  and  the  lustre  is  often  bril- 
liant. As  the  lustre  is  metallic,  it  has  been  often  supposed 
by  common  people  to  be  gold,  and  specimens  which  have 
been  found  are  every  now  and  then  taken  to  some  person 
of  known  scientific  character  in  the  community  for  in- 
quiry on  this  point.  It  has  therefore  received  the  name 
of  "  fool's  gold."  The  distinction  between  it  and  gold 
is,  however,  easily  made,  for  the  pyrites  is  very  hard,  is 
not  malleable  like  gold,  and  on  the  application  of  strong 
heat  it  gives  off  sulphurous  fumes.  It  is  not  much  prized 
as  an  ore  for  obtaining  iron,  because  of  the  difficulty  of 
ridding  it  entirely  of  the  sulphur ;  but  it  is  much  used 
for  obtaining  sulphate  of  iron  (green  vitriol  or  copperas), 
sulphuric  acid  (oil  of  vitriol),  and  sulphur.  There  is  a 
magnetic  iron  pyrites,  which  is  softer  and  liable  to  tar- 
nish. There  is  also  an  arsenical  iron  pyrites,  nearly  half 
of  which  is  arsenic.  Its  color  is  silver- white,  with  a  shin- 
ing lustre,  and  on  being  struck  with  steel  it  gives  a  spark 
with  a  garlic  odor. 

51.  Copper  Pyrites. — This  is  not  a  sulphuret  of  copper, 
but  of  copper  and  iron,  nearly  one  third  of  it  being  iron. 
It  has  a  deeper  color  than  iron  pyrites,  is  softer,  yielding 
readily  to  the  knife,  and  does  not  strike  fire  with  steel. 
Its  color  is  such  that  it  looks  like  gold,  but  it  is  at  once 
distinguished  from  it  by  its  crumbling  under  the  knife. 
Much  of  the  metal  copper  is  obtained  from  this  ore,  and 
sulphate  of  copper  (blue  vitriol)  is  largely  manufactured 
from  it.  There  is  a  copper  ore  called  copper  glance,  a 
sulphuret  in  which  the  proportion  of  iron  is  very  small. 
It  is  of  a  lead-gray  color.  There  is  also  a  sulphuret  of  a 
dark  steel-gray  color^  of  a  very  compound  character,  there 
being  in  its  composition  six  ingredients — sulphur,  copper, 
antimony,  arsenic,  iron,  zinc,  and  silver.  Sometimes  the 


SULPHUR    AND   ITS    COMPOUNDS.  35 

silver  in  it  amounts  to  30  per  cent.,  and  then  it  is  called 
argentiferous  gray  copper  ore. 

52.  Sulphuret  of  Lead. — The  common  name  of  this  min- 
eral is  galena.    Its  crystals  are  in  the  form  of  the  cube 
and  its  secondaries.     Its  color  is  lead-gray,  and  its  lustre 
is  shining.    There  is  often  sulphuret  of  silver  incorpo- 
rated with  it,  and  it  is  then  called  argentiferous  galena. 
It  is  the  ore  from  which  the  metal  lead  is  obtained,  na- 
tive lead  being  exceedingly  rare.     I  have  told  you  how 
the  galena  is  freed  from  the  sulphur  in  Part  II.,  §  193, 
and  in  §  210  how  the  silver  is  obtained  from  the  galena 
when  it  is  argentiferous.    There  are  vast  quantities  of 
galena  in  various  parts  of  the  United  States,  especially  in 
Missouri,  Illinois,  Iowa,  and  Wisconsin.     It  is  so  abund- 
ant in  the  last-named  state  that  the  miners  seldom  take 
the  trouble  to  get  out  the  ore  deeper  than  twenty-five  or 
thirty  feet.    Three  millions  of  pounds  have  been  obtained 
from  one  spot  which  is  not  over  fifty  yards  square. 

53.  Sulphuret  of  Silver. — This  mineral,  commonly  called 
silver  glance,  occurs  in  the  form  of  the  dodecahedron  and 
its  secondaries.    Its  color  is  lead-gray,  and  it  has  a  me- 
tallic lustre.    There  is  also  a  sulphuret  of  silver  and  an- 
timony, which  is  of  a  black  color,  and  therefore  is  some- 
times called  black  silver.    There  is  also  a  sulphuret  of 
silver  and  iron,  and  one  of  silver  and  copper. 

54.  Sulphuret  of  Antimony. — This  sulphuret  appear  sin 
prisms,  and  has  a  gray  color  and  metallic  lustre  very  much 
like  those  of  galena.     It  is  the  ore  from  which  is  obtained 
nearly  all  the  antimony  of  commerce.    There  are  also 
some  sulphurets  of  lead  and  antimony  combined  together. 

55.  Sulphurets  of  Arsenic. — There  are  two  sulphurets 
of  arsenic.     One  is  of  a  red  color,  is  translucent,  some- 
times transparent,  and  its  crystals  are  usually  in  the  pris- 
matic form.     It  is  called  realgar.    The  other,  called  or- 
piment,  is  of  a  lemon-yellow  color.     Both  are  used  as 
pigments,  and  also  as  coloring  substances  in  pyrotechnic 
mixtures.    They  are  obtained  chiefly  in  Koordistan  and 
China. 


36  MINERALOGY. 

56.  Sulphuret  of  Mercury. — This  is  more  abundant  than 
any  of  the  other  ores  of  mercury,  and  most  of  this  metal 
is  obtained  from  it.     It  is  called  both  cinnabar  and  ver- 
milion.   The  latter  is  its  name  as  sold  in  the  shops.    It 
is  used  as  a  pigment,  and  is  the  coloring  matter  in  red 
sealing-wax.     The  principal  mines  of  this  ore  are  in  Aus- 
tria, Spain,  Peru,  and  Upper  California. 

57.  Sulphuret  of  Zinc. — This  mineral,  commonly  called 
blende,  the  Black  Jack  of  miners,  appears  in  octahe- 
drons, dodecahedrons,  and  forms  that  are  secondary  to 
these.     It  has  a  waxy  lustre,  and  when  a  cleavage  face 
is  made  the  lustre  is  brilliant.     It  is  very  apt  to  be  found 
in  company  with  lead  ores,  and  it  abounds  in  the  lead 
mines  of  Missouri  and  Wisconsin. 

58.  The  Three  Vitriols. — The  green  vitriol  (sulphate 
of  iron),  the  blue  (sulphate  of  copper),  and  the  white 
(sulphate  of  zinc),  are  all  familiar  to  you.     They  exist  in 
nature  in  company  with  the  sulphurets  of  the  same  met- 
als, from  which  they  are  really  produced.     A  sulphate 
differs  from  a  sulphuret  in  having  oxygen  in  it,  as  you 
learned  in  Part  II.     Now  if  a  sulphuret,  of  iron  for  ex- 
ample, be  exposed  to  the  air  in  a  moist  state,  it  is  decom- 
posed, and  the  sulphur  and  the  iron,  absorbing  oxygen 
from  the  air,  become,  the  one  sulphuric  acid  and  the  oth- 
er oxyd  of  iron,  and  these  two  uniting  form  sulphate  of 
iron.     So  also  sulphate  of  copper  is  formed  from  sulphu- 
ret of  copper,  and  sulphate  of  zinc  from  sulphuret  of  zinc. 

Green  vitriol,  or  copperas,  is  largely  used  in  dyeing 
and  tanning,  because,  in  connection  with  an  ingredient  in 
nut-galls  and  many  kinds  of  bark,  it  gives  a  black  color. 
Common  ink  is  essentially  a  combination  of  copperas 
with  this  ingredient. 

59.  Sulphate  of  Lead. — This  is  usually  in  company  with 
galena,  and  is  the  result  of  its  decomposition,  after  the 
manner  indicated  in  speaking  of  the  vitriols.     Its  color  is 
white,  or  light  gray,  or  green.    Its  crystals  are  some- 
times splendid. 


SULPHUR    AND   ITS   COMPOUNDS.  3V 

60.  Gypsum. — This  is  sulphate  of  lime.  When  crys- 
tallized and  free  from  all  impurities  it  has  a  pearly  lus- 
tre, and  the  clearness  of  glass.  About  a  fifth  part  of  it 
is  water.  This  water  is  driven  off  in  preparing  it  for 
making  casts,  ornamental  work  for  walls,  etc.  The  man- 
ner of  using  it  for  these  purposes  is  described  in  §  320, 
Part  II.  Gypsum  is  a  white  and  soft  mineral,  and  ap- 
pears in  many  forms,  some  of  which  are  very  beautiful. 
One  of  these  is  the  satin  spar^  so  called  from  the  splen- 
did lustre  of  its  delicate  fibrous  arrangement.  Another, 
called  alabaster,  which  is  generally  snowy  white,  being 
compact,  with  a  fine  grain,  is  cut  into  vases  and  orna- 
ments of  various  kinds.  Sometimes  gypsum  is  composed 
of  exceedingly  thin  leaves,  laid  together  so  evenly  that  a 
multitude  of  them  make  a  crystal  clearer  than  the  clear- 
est glass.  The  name  selenite,  which  has  been  given  to 
this  and  some  other  varieties  of  gypsum,  comes  from  se- 
lene,  the  Greek  word  for  moon.  There  is  an  anhydrous 
sulphate  of  lime,  that  is,  one  which  has  no  water  incor- 
porated with  it,  the  term  coming  from  two  Greek  words, 
aw,  without,  and  udor,  water.  Gypsum  occurs  abundant- 
ly in  many  parts  of  this  country.  Fine  specimens  are 
found  near  Lockport,  New  York.  As  before  noticed  (§ 
1 6),  in  the  Mammoth  Cave  of  Kentucky  alabaster  appears 
with  its  crystals  arranged  in  various  forms  of  flowers, 
branches  of  shrubbery,  vines,  etc. 

Common  limestone  has  sometimes  been  mistaken  for 
gypsum  by  persons  who  are  ignorant  of  chemistry  and 
mineralogy.  Professor  Hitchcock  relates  a  case  of  this 
kind.  A  farmer  supposed  that  he  had  found  gypsum  on 
his  farm,  and  his  neighbors,  believing  it,  bought  large 
quantities  of  the  material  for  agricultural  purposes.  Aft- 
er grinding  up  a  considerable  amount  of  it,  some  one  ac- 
cidentally discovered  that  it  was  limestone.  The  error 
might  have  been  avoided  by  simply  testing  the  sub- 
stance with  acid.  A  drop  would  have  occasioned  an  ef- 
fervescence, showing  that  it  was  carbonate,  and  not  sul- 


38  MINERALOGY. 

phate  of  lime,  the  acid  taking  the  lime  to  itself,  .and  set- 
ting free  the  carbonic  acid  gas.     See  §  60,  Part  II. 

61.  Sulphates  of  Magnesia  and  Soda. — The   slender, 
spicula-like  crystals  of  Epsom  salts  (sulphate  of  magne- 
sia), which  are  probably  familiar  to  you,  are  prisms.   Mi- 
nute crystals  of  this  mineral  are  often  present  in  the 
earth  on  the  floors  of  the  limestone  caves  in  the  western 
part  of  this  country.     In  the  Mammoth  Cave  of  Ken- 
tucky feathery  masses  of  the  crystals  adhere  to  the  roof, 
looking  like  snow-balls.     The  common  name  of  this  min- 
eral came  from  the  fact  that  at  Epsom,  in  England,  the 
waters  of  the  springs  hold  it  in  solution.     The  crystals 
of  Glauber's  salt  are  also  prisms,  but  they  are  coarse 
compared  with  those  of  Epsom  salts.    Both  of  these 
salts  are  present  in  sea-water. 

62.  Sulphate  of  Baryta. — This  is  so  heavy  a  mineral 
that  it  is  called  heavy  spar.     The  crystals,  which  are 
translucent,  sometimes  transparent,  are  often  very  beau- 
tiful.   It  is  found  abundantly  in  some  localities  in  this 
country,  as  Cheshire,  Conn. ;  Pillar  Point,  N.  Y. ;  near 
Fredericksburg,  Va.     It  is  extensively  ground  up  for  use 
in  paints,  being  mixed  with  white  lead.     The  mixture 
has  various  names,  according  to  the  proportions  of  the 
various  ingredients :  Venice  White,  when  there  are  equal 
parts  of  the  two ;  Hamburg  White,  when  the  lead  is  half 
the  weight  of  the  sulphate  of  baryta ;  and  Dutch  White, 
when  it  is  one  third. 

.63.  Sulphuric  and  Sulphurous  Acids. — That  intense 
acid,  sulphuric  acid,  or  oil  of  vitriol,  as  it  is  commonly 
called,  is  occasionally  found  near  volcanoes  and  sulphur 
springs.  Sulphurous  acid,  the  pungent  and  suffocating 
gas  which  is  produced  whenever  sulphur  is  burned,  is 
often  very  abundant  about  volcanoes  when  they  are  in 
action. 

64.  Sulphureted  Hydrogen.— This  very  offensive  gas  is 
common  at  sulphur  springs,  and  it  is  by  its  agency  that 
articles  of  silver  are  so  readily  blackened  in  such  locali- 


METALS   AND   THEIR    ORES.  39 

ties,  the  sulphur  of  the  gas  uniting  with  the  silver  to  form 
a  sulphuret  of  that  metal.  This  gas  is  also  sometimes 
generated  about  volcanoes. 


CHAPTER  V. 

METALS   AND   THEIR   ORES. 

65.  Native  Metals. — A  metal  is  said  to  occur  native 
when  it  is  found  either  pure  or  mingled  with  some  other 
metal  in  the  form  of  an  alloy ;  in  other  words,  when  it  is 
not  united  chemically  with  any  other  substance. 

66.  Ores. — When  a  metal  is  united  chemically  with 
any  substance,  the  compound  is  called  an  ore.    The  metal 
is  in  this  case  said  to  be  mineralized.    The  most  common 
of  these  compounds  are  sulphurets,  oxyds,  and  carbon- 
ates.   The  word  ore  is  sometimes  used  in  a  less  strict, 
sense  for  alloys,  and  even  native  metals  are  often  termed 
ores.     On  the  other  hand,  it  is  proper  to  state  that  to 
the  compounds  of  some  of  the  metals  the  term  is  not  ap- 
plied at  all.     I  refer  to  the  earths  and  alkalies,  which  are 
combinations  of  certain  metals  with  oxygen,  to  their 
salts,  and  to  the  combinations  of  these  same  metals  with 
chlorine,  iodine,  etc.     These  metals,  potassium,  sodium, 
etc.,  have  been  discovered  comparatively  at  a  recent  date, 
are  never  found  native,  and,  when  obtained  by  chemical 
processes,  are,  most  of  them,  preserved  in  their  metallic 
state  with  difficulty.     You  see,  then,  the  propriety  of  not 
calling  their  compounds  ores.     It  is  to  the  compounds 
of  the  well-known  metals  only  that  the  term  is  applied. 

67.  Positions  and  Associations  of  Ores.— The  ores  of 
metals  are  sometimes  scattered  here  and  there  in  rocks, 
in  collections  small  and  large ;  but  commonly  they  are 
in  veins,  or  lodes,  as  they  are  called,  or  in  layers  between 
layers  of  rock.     They  are  associated  with  quartz,  carbon- 
ate of  lime,  and  various  other  minerals.     Often  two  or 
more  different  ores  are  mingled  together. 


40  MINERALOGY. 

68.  Obtaining  Metals  from  their  Ores. — Sometimes  this 
is  a  very  simple  process.     For  example,  in  the  case  of 
bismuth,  all  that  is  necessary  is  to  heat  the  pounded  ore, 
and  the  melted  metal  runs  out.     So,  if  you  have  a  sul- 
phuret  of  lead,  or  mercury,  or  antimony,  heat  will  fully 
decompose  the  compound,  driving  off  the  sulphur.     But 
sometimes  the  use  of  some  other  substance  is  required 
for  the  decomposition  of  the  ore.     Thus,  if  we  have  an 
oxyd  of  iron,  we  heat  it  with  charcoal.     Here  the  oxygen 
quits  the  iron  to  unite  with  the  carbon,  forming  carbonic 
acid,  which  flies  off,  leaving  the  metallic  iron. 

69.  Gangues  and 'Impurities. — The  rock  in  which  an 
ore  is  found  is  called  the  gangue.     Much  of  this  is  separ- 
ated from  the  ore  in  collecting  it,  and  much  more  of  it, 
perhaps,  by  the  process  called  washing,  in  which  the  ma- 
terial, coarsely  powdered,  is  subjected  to  a  current  of 
water,  that  washes  away  the  lighter  pieces,  leaving  those 
which  are  rendered  heavy  by  the  presence  of  the  metal. 
The  impurities  which  are  often  mingled  with  ores  are 
got  rid  of  in  various  ways.     Sometimes^/tees,  so  called, 
are  used  for  this  purpose.     This  is  done  with  most  iron 
ores.     There  is  commonly  mixed  with  these  ores  quartz 
or  clay ;  and  as  quartz  is  pure  silica,  and  silica  consti- 
tutes 75  per  cent,  of  clay,  the  ore  is  reduced  by  strongly 
heating  it  together  with  a  substance  which  will  form  a 
silicate,  that  is,  a  glass,  w^th  the  silica  (§  342,  Part  II.). 
Such  a  substance  is  common  limestone. 

Other  processes  will  be  noticed  hereafter  in  the  case 
^of  particular  ores. 

70.  Iron. — The  most  common  of  the  ores  of  this  metal 
are  oxyds  and  sulphurets.     Of  the  latter  I  have  already 
spoken  in  §  50.     Its  ores  are  more  abundant  in  the  earth 
than  those  of  any  other  metal,  because  it  is  the  most  ex- 
tensively and  variously  useful  of  all  the  metals.     They 
are  the  common  coloring  ingredients  of  rocks,  and  there- 
fore of  soils.     Red  and  yellow  are  the  most  frequent  col- 
ors, but  they  color  also  a  dull  green,  brown,  and  black. 


METALS    AND   THEIR    ORES.  41 

Iron  is  present  in  a  small  amount  in  many  vegetable  and 
animal  substances,  and  in  our  blood  it  is  an  essential, 
though  a  minute  ingredient  (§  663,  Part  IL). 

71.  Meteoric  Iron. — Native  iron  has  not  been  ascer- 
tained to  occur  except  in  meteorites,  and  there  it  is  al- 
loyed with  nickel,  and  with  a  small  amount  of  other  met- 
als— tin,  cobalt,  copper,  and  manganese.     The  mass  in 
the  cabinet  of  Yale  College,  from  Texas,  weighing  1635 
pounds,  contains  from  90  to  92  per  cent,  of  iron,  and  from 
8  to  10  per  cent,  of  nickel,  the  mixture  of  the  two  metals 
not  being  uniform  throughout  the  mass.     There  is  one 
mass  of  meteoric  iron  in  South  America  which  is  sup- 
posed to  weigh  30,000  pounds. 

72.  Magnetic  Iron  Ore. — This  ore  has  this  name  from 
its  magnetic  properties.     It  is  an  oxyd  of  iron,  of  an  iron- 
black  color,  generally  in  granular  masses,  but  sometimes 
in  distinct  crystals,  which  are  octahedrons  or  dodecahe- 
drons, or  their  secondary  forms.     This  very  superior  ore 
of  iron  is  as  widely  disseminated  as  any  ore  of  this  met- 
al.    Nearly  all  the  Swedish  iron  ore  is  of  this  kind.     In 
Sweden  and  Lapland  there  are  mountains  of  it.     When 
a  mass  of  this  ore  is  in  a  state  of  magnetic  polarity  it  is 
a  lodestone  or  natural  magnet.     The  lodestone  was  first 
found  in  the  province  of  Magnesia,  and  was  called  mag- 
nes  by  Pliny,  and  hence  the  terms  magnet  and  magnetism. 

73.  Hematite. — This,  like  thp  magnetic  iron  ore,  is  an 
oxyd,  but  is  distinguished  from  it  by  its  powder  being 
red.     It  is  this  which  has  given  it  its  name,  from  the 
Greek  word  haima,  blood.     This  mineral  appears  in  va- 
rious forms,  generally  in  granular  mass,  in  Iamina3,  or 
earthy,  and  easily  powdered.    What  is  called  red  chalk  is 
one  of  the  varieties.     This  ore  is  abundant  in  this  coun- 
try.    The  two  iron  mountains  in  Missouri  consist  for  the 
most  part  of  this  ore  piled  up  "in  masses  of  all  sizes,  from 
a  pigeon's  egg  to  a  middle-sized  church." 

74.  Limonite,  or  Brown  Iron  Ore. — This  is  not  merely 
an  oxyd  of  iron,  but  a  hydrated  oxyd,  containing  water 


42  MINERALOGY. 

to  about  14  per  cent.  One  of  its  forms  is  yellow  ochre, 
which  is  used  as  a  common  material  in  paint.  The  pow- 
der of  this  ore  is  also  used  for  polishing  metallic  surfaces. 
75.  Chromic  Iron. — This  mineral  is  composed  chiefly 
of  the  oxyds  of  two  metals,  iron  and  chromium.  The 
oxyd  of  the  latter  acts  as  an  acid,  as  mentioned  in  §  301, 
Part  II.,  and  the  mineral  is  therefore  said  to  be  a  chro- 
mate  of  iron.  There  are,  however,  two  other  compo- 
nents, alumina  and  magnesia,  which  vary  in  quantity  in 
different  specimens.  This  mineral  is  quite  abundant  at 
Barehills,  near  Baltimore,  in  Lancaster  county,  Pennsyl- 
vania, and  several  other  places  in  this  country.  Its  crys- 
tals are  octahedrons.  It  is  valuable  in  the  manufacture 
of  the  chrome  pigments,  of  which  the  chrome  yellow  is 
the  principal. 

76.  Carbonate  of  Iron. — This  miner- 
al varies  in  color  from  light  gray  to 
dark  brown  or  nearly  black  on  ex- 
posure. Its  crystals  sometimes  have 
curved  faces,  as  represented  in  Fig. 
21.  Metallic  iron  is  extensively  ob- 
tained  from  this  ore. 
77.  Native  Copper. — This  occurs  in  company  with  ores 
of  the  metal,  commonly  in  the  neighborhood  of  igneous 
rocks — that  is,  rocks  which  have  been  made  and  thrust 
upward  in  the  crust  of  tl^  earth  by  the  agency  of  heat. 
There  is  often  silver  with  the  copper,  either  intimately 
mixed  with  it,  making  an  alloy,  or  collected  by  itself  in 
small  masses  or  in  strings.  Copper  is  next  to  iron  in 
abundance.  There  are  famous  mines  in  Cornwall,  En- 
gland, in  Brazil,  and  in  Siberia.  Perhaps  the  most  ex- 
traordinary copper  region  in  the  world  is  in  the  vicinity 
of  Lake  Superior.  It  is  found  there  in  veins  filling  up 
fissures  in  the  rocks,  and  it  is  cut  out  in  monstrous  blocks 
with  chisels  and  drills.  One  mass,  weighing  nearly  4000 
pounds,  was  carried  to  Washington,  and  a  large  mass  has 
been  since  got  out  which  was  estimated  to  weigh  200 


METALS    AND   THEIR    ORES.  43 

tons.  As  you  will  see  in  another  part  of  this  book,  the 
geologist  has  found  clear  proof  that  the  native  copper  of 
this  region  was  produced  in  Nature's  great  furnaces  from 
ores  of  the  metal  ages  upon  ages  before  the  creation  of 
man. 

The  sulphurets  of  copper  and  the  sulphate  were  no- 
ticed in  the  preceding  chapter.  I  go  on  now  to  notice 
the  principal  of  the  other  ores  of  this  metal. 

78.  Oxyds  of  Copper. — There  are  two  oxyds,  a  red  and 
a  black  one.     The  metal  can  be  obtained  from  them  by 
heating  with  charcoal,  the  oxygen  uniting  with  the  car- 
bon to  form  carbonic  acid  gas,  which  flies  off. 

79.  Carbonates  of  Copper. — There  are  two  carbonates. 
One  of  them,  called  malachite,  is  of  a  light  green  color, 
and,  as  it  is  capable  of  a  high  polish,  it  is  used  in  various 
ways  for  ornamental  articles.     Its  value,  when  manufac- 
tured as  veneering  or  inlaid  work,  is  about  three  guineas 
per  pound,  and  there  are  at  least  two  pounds  and  a  half 
in  a  square  foot  of  finished  work.     In  Russia,  where  large 
pieces  of  it  can  TDC  obtained,  slabs  for  tables,  mantle- 
pieces,  vases,  etc.,  are  made  from  it.     The  blue  carbonate 
sometimes  presents  splendid  crystals. 

80.  Silicate  of  Copper. — This  mineral,  a  compound  of 
silica  or  silicic  acid  with  oxyd  of  copper,  has  a  bluish- 
green  color.     Sometimes  the  green  carbonate  and  this 
silicate  are  united  in  one  mineral. 

81.  Lead. — Native  lead  is  exceedingly  rare.     Its  most 
common  ore,  galena,  and  the  sulphate  I  noticed  in  the 
preceding  chapter.     The  oxyd  of  lead,  minium,  is  what 
is  commonly  called  red  lead.     The  carbonate  is  the  white 
lead  of  commerce.     The  chromate  of  lead  is  the  chrome 
yellow  used  by  painters. 

82.  Tin. — The  native  metal  is  exceedingly  rare.     The 
chief  ore  is  an  oxyd,  the  sulphuret  being  seldom  found. 
This  is  an  ingredient  in  pewter  and  bronze,  and  in  the 
amalgam  put  on  the  backs  of  mirrors,  and  some  of  its 
salts  are  employed  in  dyeing.     The  tin  used  in  making 


44  MINERALOGY. 

tin- ware  is  iron  in  the  form  of  sheets  covered  with  tin, 
which  does  not  oxydize  as  readily  as  tin  does.  The  chief 
tin  mines  are 'at  Cornwall,  in  England,  in  the  island  of 
Banca,  in  Malacca,  and  in  Austria.  It  is  supposed,  from 
some  allusion  in  ancient  history,  that  the  Cornwall  mines 
were  worked  some  centuries  before  the  Christian  era. 

83.  Zinc. — This  metal  never  occurs  native.     I  have  al- 
ready noticed  its  chief  ore,  the  sulphuret,  in  §  57,  and  the 
sulphate  in  §  58.     The  other  ores  which  are  at  all  promi- 
nent are  the  red  oxyd  and  the  carbonate.     For  the  uses 
of  this  metal  I  refer  you  to  §  198,  Part  II. 

84.  Antimony. — This  metal  is  occasionally  found  na- 
tive.    Its  usual  combinations  are  with  sulphur,  or  with 
sulphur  and  lead  together.     It  is  sometimes  also  com- 
bined with  oxygen,  arsenic,  lime,  nickel,  silver,  and  cop- 
per.    The  chief  use  of  the  metal  is  in  the  composition  of 
type-metal.     In  medicine  there  is  used  a  double  salt,  in 
which  antimony  is  one  of  the  bases,  the  tartrate  of  anti- 
mony and  potash. 

85.  Cobalt. — There  are  two  arsenical  ores  of  this  met- 
al— that  is,  ores  in  which  it  is  combined  with  arsenic. 
Zaffre  is  a  beautiful  coloring  material  prepared  from  the 
ores  of  cobalt.     Smalt  is  glass  colored  with  zaffre  and 
reduced  to  a  fine  powder.     This  is  used  to  give  a  deli- 
cate blue  tinge  to  writing  paper  and  to  linen. 

86.  Nickel. — Native  nickel  is  never  of  terrestrial  or- 
igin, but  it  is  one  of  the  ingredients  in  the  alloy  which 
we  have  in  meteorites,  as  stated  in  §  71.    It  has  two  ar- 
senical ores,  a  carbonate,  various  compound  sulphurets, 
etc.      German  silver,  so  called,  is  an  alloy  of  copper, 
nickel,  and  zinc. 

87.  Bismuth. — This  is  found  native,  and  also  combined 
with  oxygen,  carbonic  acid,  silica,  and  the  metal  tellu- 
rium.    It  is  an  ingredient  in  the  most  superior  kind  of 
type-metal,  in  the  "  mosaic  gold,"  and  in  an  alloy  used 
in  soldering  pewter.     Most  of  it  comes  from  one  locality, 
Schneeberg,  in  Saxony,     It  is  obtained  from  the  rocks 


METALS    AND   THEIR    OSS^gOSff^^  45 

in  which  it  is  present  by  powdering  coarsely,  and  then 
exposing  to  strong  heat  in  a  kiln.  The  bismuth  is  melt- 
ed only,  and  runs  into  a  trough  at  the  bottom. 

88.  Manganese. — The  ores  of  this  metal  are  some  of 
them  composed  of  but  two  ingredients,  as  the  oxyds  and 
sulphurets;  and  others  are  very  compound,  containing 
silica,  iron,  lime,  magnesia,  etc.     The  peroxyd  is  used  by 
the  chemist  for  obtaining  oxygen  gas,  and  is  employed 
largely  in  bleaching.     Some  of  the  salts  of  this  metal  are 
used  in  calico  printing.     Manganese  gives  a  violet  color 
to  glass. 

89.  Mercury. — This  is  the  only  metal  that  is  liquid  in 
all  ordinary  temperatures.     It  becomes  solid  at  39°  be- 
low zero,  and  therefore  can  not  be  used  in  thermometers 
in  the  arctic  regions.     It  crystallizes  in  cubes.     It  is 
sometimes  found  native,  commonly  in  globules  scattered 
here  and  there,  but  sometimes  in  such  quantities  that  it 
can  be  dipped  up  in  pails.     It  is  related  that  the  mines 
of  mercury  in  Mexico  were  discovered  by  a  hunter,  who, 
as  he  clambered  up  a  mountain,  caught  hold  of  a  shrub, 
which,  giving  way  at  the  root,  let  out  a  stream  of  what 
he  supposed  was  liquid  silver.     The  rapidity  with  which 
this  metal  runs,  occasioned  by  its  great  weight,  gave  to 
it  the  name  of  quicksilver.     The  purity  of  the  mercury 
is  judged  of  by  the  workmen  by  watching  it  as  it  is 
dropped  upon  glass.     If  in  running,  instead  of  preserv- 
ing fully  its   characteristic  globular  shape,  it  forms  a 
queue,  or  drags  a  tail,  as  it  is  expressed,  there  is  lead  or 
some  other  impurity  present.     Mercury  is  used  in  a  va- 
riety of  ways.     It  is  the  liquid  used  in  barometers,  and 
generally  in  thermometers.     It  is  used  for  silvering  mir- 
rors, an  amalgam  being  formed  with  tin  for  this  purpose. 
Its  disposition  to  amalgamate  with  other  metals  is  made 
use  of  extensively  in  extracting  gold  and  silver  from  the 
impurities  with  which  they  are  mixed,  as  described  in  § 
213,  Part  II.     Then  there  are  various  preparations  and 
combinations  of  this  metal  employed  in  medicine.    The 


46  MINEEALOGY. 

most  common  ore  of  mercury,  the  sulphuret,  was  noticed 
in  §  56. 

90.  Silver. — This  metal  is  found  pure,  in  alloy,  and  in 
chemical  combination  with  sulphur,  arsenic,  chlorine,  va- 
rious acids,  etc.     When  it  is  found  native  it  is  not  usu- 
ally alone,  but  is  alloyed  with  copper,  and  sometimes 
with  gold.     The  copper  in  the  alloy  sometimes  amounts 
to  10  per  cent.    The  chief  ores  of  silver,  the  sulphur ets, 
were  noticed  in  §  53. 

91.  Gold. — This  metal  has  no  disposition  to  unite  with 
oxygen  or  with  other  elements,  and  therefore  is  found 
in  nature  either  pure,  or  alloyed  with  some  other  metals, 
chiefly  silver  and  copper.     The  only  chemical  compound 
formed  by  gold  in  nature  is  with  tellurium,  termed  a  tel- 
lurid  of  gold,  and  this  is  quite  rare.     As  you  have  al- 
ready learned,  iron  and  copper  pyrites  have  often  been 
supposed  to  be  gold  by  those  who  are  ignorant  in  regard 
to  minerals.     But  the  distinction  is  easily  made,  for  gold 
flattens  out  on  being  hammered,  and  is  readily  cut,  while 
the  pyrites  break  in  pieces  on  being  hammered,  and  nei- 
ther of  them  can  be  cut  in  slices,  no  impression  even  be- 
ing made  by  the  knife  on  the  iron  pyrites.     Besides,  the 
pyrites,  on  being  exposed  to  a  strong  heat,  emit  a  sul- 
phureous odor,  while  the  melting  gold  is  odorless.     Gold 
is  commonly  found  in  grains  or  rounded  masses  of  vari- 
ous sizes,  but  sometimes  it  is  crystallized  in  the  form  of 
the  cube  or  octahedron.     Sometimes  large  lumps  have 
been  found.     The  largest  lump  that  has  yet  been  ob- 
tained was  from  California.     It  furnished  109  pounds 
and  4  ounces  of  pure  gold.    Gold  is  diffused  in  most 
countries  in  small  quantities ;  but  there  are  some  locali- 
ties where  it  abounds,  as  the  Urals,  Hungary,  Spain,  va- 
rious parts  of  South  America  and  Africa,  but  especially 
Australia  and  California.     In  these  two  last  localities  it 
was  discovered  but  recently — in  California  in  1848,  and 
in  Australia  in  1851.     A  locality  along  the  coast  of  Afri- 
ca, opposite  Madagascar,  has  been  supposed  to  be  the 


METALS   AND   THEIR   ORES.  47 

Ophir  of  Solomon's  time.  The  Russian  mines,  that  is, 
those  of  the  Urals  and  Siberia,  were,  till  of  late,  the  lar- 
gest sources  of  gold,  but  the  mines  of  California  and  Aus- 
tralia far  surpass  them ;  and  it  is  stated  by  Professor 
Dana  that  "  the  whole  product  of  Europe,  Asia,  Africa, 
and  South  America  is  far  less  at  the  present  time  than 
is  derived  from  Australia  or  the  United  States." 

92.  Modes  of  Obtaining  Gold. — If  the  gold  be  in  rock, 
this  is  pounded  up  and  sifted,  and  the  sand  thus  obtained 
washed  in  a  pan.  The  gold  being  seven  times  heavier 
than  the  same  bulk  of  sand  or  gravel,  those  portions  of 
the  sand  which  have  gold  attached  to  them  subside  to 
the  bottom  of  th£  pan,  while  the  other  portions,  being 
lighter,  run  off  with  the  water.  The  portions  which 
subside  are  subjected  to  the  amalgamation  process,  in 
which  mercury  unites  with  the  gold,  forming  an  amal- 
gam, and  thus  separates  the  metal  from  the  sand.  The 
gold  is  then  obtained  from  the  amalgam  by  means  which 
are  detailed  in  §  213,  Part  II.,  where  the  whole  process 
is  fully  described.  This  sorting  of  gold  by  washing  is 
carried  on  extensively  in  nature  in  the  alluvial  washings, 
as  they  are  called.  The  grains  and  scales  found  in  the 
gravel  and  sand  in  the  beds  of  streams  and  on  their  bor- 
ders were  once  in  rocks,  which  were  worn  away  by 
means  that  will  be  made  clear  to  you  in  another  part  of 
this  book.  The  gold,  on  account  of  its  weight,  is  always 
lagging  behind  the  materials  that  accompany  it  at  the 
start ;  and  the  larger  are  the  pieces  of  the  metal,  the  less 
distance  are  they  carried,  for  small  pieces  have  a  larger 
surface  in  proportion  to  their  weight  for  the  water  to 
act  upon  (§  193,  Parti.).  For  the  same  reason,  a  round 
piece  is  not  carried  as  far  as  a  scale.  When  there  is  a 
rock  in  the  path  of  a  stream,  the  pieces  of  gold  collect 
there,  the  lighter  gravel  and  sand  being  carried  along 
by  the  water.  The  formation  of  this  "pocket"  of  gold 
is  very  much  like  the  gathering  of  the  golden  grains  in 
the  bottom  of  the  pan  in  artificial  washing.  Sometimes, 


48  MINERALOGY. 

on  the  borders  of  a  stream,  the  material  which  has  been 
drifted  down  previously  .may  have  much  gold  in  it.  To 
bring  it  to  light,  the  stream  is  turned  across  it,  to  per- 
form on  a  large  scale  the  same  operation  of  washing  that 
is  done  in  a  small  way  with  the  pan.  The  processes 
necessary  for  separating  the  gold  when  it  is  alloyed  with 
silver  or  copper  I  will  not  stop  to  describe. 

93.  Uses  of  Gold. — The  usefulness  of  this  metal  results 
from  its  malleability,  its  ductility,  its  rich  color,  its  sus- 
ceptibility of  a  high  polish,  and  its  indisposition  to  tarnish 
on  exposure.    A  gold-beater  can  hammer  a  grain  of  gold 
into  a  leaf  covering  a  space  of  50  square  inches,  and  its 
thickness  is  only  the  282,000th  of  an  inch.     Its  ductility 
equals  its  malleability,  as  is  shown  in  the  wire  of  gold 
lace.     It  is  from  these  two  qualities  that  gilding  is  so 
cheap,  and  therefore  so  common,  thereby  making  this 
costly  metal  a  great  convenience  to  the  people  at  large. 
For  ordinary  uses,  gold  is  alloyed  with  silver  and  copper 
to  give  it  the  requisite  hardness.     The  standard  gold  of 
the  United  States  contains  nine  parts  of  pure  gold  to 
one  of  alloy.     The  word  carat,  used  so  often  in  speaking 
of  the  purity  of  gold  in  the  market,  means  one  twenty- 
fourth  ;  so  that  if  any  specimen  is  said,  for  example,  to 
be  twenty  carats  fine,  it  is  meant  that  the  pure  gold  is  to 
the  alloy  as  20  to  4,  and  so  of  other  proportions. 

94.  Platinum  and  its  Associate  Metals. — Platinum  is 
seldom  found  alone,  but  is  commonly  mingled  with  more 
or  less  of  certain  rare  metals — iridium,  rhodium,  palla- 
lium,  and  osmium — and  such  common  metals  as  iron 
and  copper.     It  occurs  usually  in  small  grains,  but  some- 
times is  found  in  pieces  of  considerable  size.     The  lar- 
gest mass  that  has  yet  been  found  weighed  21  pounds 
Troy.     Platinum  is  often  spoken  of  as  being  the  heavi- 
est substance  known,  but  there  is  one  metal,  iridium, 
that  is  a  very  little  heavier.     Its  color  is  between  that 
of  tin  and  steel,  though  in  the  alloys  in  which  it  is  usu- 
ally found  it  is  darker  than  this.     It  is  very  malleable, 


OXY-SALTS   AND    HALOID   SALTS.  49 

especially  when  heated.  Its  ductility  is  so  great  that 
Dr.  Wollaston  succeeded  in  making  a  wire  of  it  the  two 
thousandths  (-^oVo)  of  an  inch  in  diameter.  In  fusibility 
this  metal  and  mercary^  stand  at  opposite  ends  of  the 
scale.  While  mercury  may  be  said  to  melt  at  39°  be- 
low zero,  platinum  can  not  be  melted  in  the  hottest 
furnace,  as  is  shown  in  the  crucibles  of  the  chemist  that 
are  made  of  it.  The  metals  iridium,  rhodium,  and  os- 
mium, which  are  found  in  company  with  platinum,  are 
very  hard,  and  are  used  for  points  to  gold  pens.  There 
is  a  mineral  called  iridosmine,  because  composed  of  irid- 
ium and  osmium,  which  is  the  hardest  alloy  known. 
This  mineral,  which  is  found  in  scales,  is  also  used  for 
pointing  gold  pens. 


CHAPTER  VI. 

OXY-SALTS   AND   HALOID   SALTS. 

95.  The  two  Classes  of  Salts. — Those  salts  which  are 
formed  by  the  union  of  acids  with  oxyds  are  called  oxy- 
salts,  because  they  have  oxygen  in  their  composition. 
There  is,  besides,  a  class  of  salts  which  contain  no  oxy- 
gen, but  are  composed  of  a  metal  and  some  other  element. 
Common  salt  is  an  example.    This  is  composed  of  chlo- 
rine and  sodium,  and  is  a  chlorid  of  sodium.     This  is  the 
principal  salt  of  this  class,  and  hence  the  name  given  to 
the  whole  class,  haloid,  from  two  Greek  words,  hols,  sea- 
salt,  and  eidos,  like.     Some  of  the  oxy-salts  have  been  al- 
ready treated  of  in  other  connections,  as  the  sulphates  in 
the  chapter  on  sulphur  and  its  compounds,  from  their 
natural  association  with  the  sulphurets.   'There  are  also 
some  which  will  be  reserved  for  another  chapter,  as  the 
silicates,  on  the  same  principle  of  natural  grouping. 

96.  Nitrate  of  Potash. — This  salt,  commonly  called  ni- 
tre or  saltpetre,  is  produced  in  India  and  South  America 
from  the  decomposition  of  animal  substances  in  the  soil 

C 


50  MINERALOGY. 

in  hot  and  dry  weather  succeeding  a  rain.  It  is  also  pro- 
duced in  the  same  way  in  Egypt,  and  appears  in  light 
tufts,  which  are  gathered  up  by  a  sort  of  broom,  and 
the  nitre  is  separated  from  its  impurities  by  lixiviation, 
and  is  crystallized  by  evaporation.  It  is  found  diffused 
in  the  earth  on  the  floor  of  some  of  our  Western  caverns, 
and  is  apt  to  appear  in  crusts  or  needle-like  crystals  on 
their  walls.  This  salt  is  that  one  of  the  ingredients  of 
gunpowder  that  furnishes  the  oxygen  required  for  the 
combustion. 

97.  Nitrate  of  Soda. — This  is  very  much  like  nitre;  like 
that,  it  deflagrates  when  thrown  upon  the  fire,  and  it  has 
the  same  supply  of  oxygen  in  it  that  nitre  has ;  and  it 
would  answer  the  purpose  equally  well  in  gunpowder  if 
it  did  not  readily  deliquesce — that  is,  gather  moisture 
from  the  atmosphere.     Both  this  salt  and  the  nitre  are 
used  for  obtaining  nitric  acid. 

98.  Common  Salt. — This  is  composed  of  chlorine  and 
sodium,  two  elements  which  never  appear  in  nature  un- 
combined.    Its  crystals  are  the  cube  and  its  secondaries. 
A  peculiarity  in  the  arrangement  of  its  crystals  when 
they  are  formed  in  a  solution  was  shown  in  §  22.    This 
mineral  is  very  thoroughly  diffused  in  the  earth,  mostly, 
however,  in  solution,  nearly  one  thirtieth  of  all  the  water 
in  the  sea  being  common  salt.     Lakes  that  have  no  outlet 
to  the  sea  are  very  salt.    This  is  the  case  with  the  Great 
Salt  Lake  of  this  country,  the  Dead  Sea,  and  the  Caspian 
Sea.     Over  one  fifth  of  the  water  of  the  Great  Salt  Lake 
is  salt,  and  the  proportion  is  even  greater  in  the  case  of 
the  Dead  Sea.     There  are  famous  salt  mines  where  the 
solid  mineral  is  obtained  in  Poland,  Hungary,  Spain,  Sici- 
ly, and  Switzerland.    In  the  extensive  mines  near  Cracow 
chapels,  halls,  etc.,  are  excavated  far  below  the  surface, 
their  roofs  being  supported  by  immense  pillars  of  salt, 
which,  on  being  lighted  up,  present  a  magnificent  ap- 
pearance.   In  Northern  Africa  there  are  hills  of  salt.    In 
this  country  vast  quantities  of  salt  are  obtained  by  evap- 


OXY-SALTS   AND    HALOID    SALTS.  51 

oration  from  the  water  of  salt  springs.  The  springs  in 
Onondago  county,  New  York,  are  the  most  productive, 
one  seventh  part  of  the  water  being  salt.  In  hot  climates 
much  salt  is  obtained  from  sea  water  by  evaporation. 
The  manner  in  which  this  is  done  is  described  in  §  358, 
Part  II. 

99.  Borate  of  Soda.— Nearly  half  (47  per  cent.)  of  this 
salt,  commonly  called  borax,  is  water.     It  abounds  in  a 
lake  in  Thibet,  where  it  is  literally  dug  out  from  the  bor- 
ders and  shallow  places.     As  the  borax  is  deposited  from 
the  water,  the  holes  made  in  gathering  it  are  soon  filled 
up.     This  lake  is  at  so  high  an  elevation  that  it  is  frozen 
over  the  greater  part  of  the  year.     The  acid  which  en- 
ters into  the  composition  of  borax,  boracic  acid,  is  some- 
times found  in  the  vicinity  of  volcanoes,  exhaling  from 
springs  in  the  earth.     It  is  present  in  the  hot  vapors  of 
the  lagoons  in  Tuscany,  from  which  it  is  obtained  by  let- 
ting the  vapor  pass  into  cold  water  to  condense  it,  and 
then  allowing  the  solution  to  evaporate.     This  leaves  the 
boracic  acid  in  large  crystalline  flakes. 

100.  Carbonate  of  Lime. — This  mineral,  in  the  forms  of 
common  limestone,  chalk,  and  marble,  constitutes  about 
one  seventh  part  of  the  crust  of  the  globe,  and  therefore 
will  be  brought  quite  largely  to  your  notice  in  the  geo- 
logical part  of  this  book.     There  are  mountains  made  of 
it,  and  there  are  extensive  deposits  of  it  in  layers  of  rock. 
It  appears  also  in  smaller  quantities  in  many  other  forms, 
some  of  them  exceedingly  beautiful.     It  is  readily  distin- 
guished from  other  minerals  by  dropping  some  acid,  as 
the  sulphuric,  upon  it,  this  occasioning  an  effervescence 
by  uniting  with  the  lime  and  setting  free  the  carbonic 
acid,  as  already  stated  in  §  60.     Exposed  to  a  red  heat 
the  carbonic  acid  is  driven  off,  and  we  have  the  lime  left 
alone.     This  is  what  is  done  in  the  lime-kiln,  and  it  is  in 
this  way  that  the  lime  used  for  making  mortar  and  other 
purposes  is  obtained.     Hydraulic  lime,  which  has  this 
name  because  it  will  "set"  under  water,  is  made  from 


52  MINERALOGY. 

limestone  in  which  there  are  some  silica  and  clay,  and 
sometimes  magnesia.  Marl,  which  is  of  so  great  use  in 
agriculture,  is  a  mixture  of  carbonate  of  lime  with  clay. 
When  carbonate  of  lime  is  deposited  from  the  waters  of 
a  mineral  spring  it  is  called  calcareous  tufa.  Crystalli- 
zation is  prevented  in  this  case  from  the  constant  mo- 
tion of  the  water.  Chalk,  though  abundant  in  England, 
France,  and  many  other  countries,  is  not  found  at  all  in 
this  country,  though  the  other  common  forms  of  carbon- 
ate of  lime  are  present  in  large  quantities. 

101.  Calcareous  Spar. — This  name  is  usually  given  to 
the  crystallized  varieties  of  carbonate  of  lime.     The  crys- 
tals vary  exceedingly  from  the  variety  of  their  secondary 
forms.     Some  fanciful  names  are  given  to  some  of  them 
from  their  peculiar  shapes,  as  dog-tooth  spar  and  nail- 
head  spar.     They  are  various  in  color,  commonly  white 
or  light  gray,  or  reddish  or  yellowish,  and  sometimes 
wine-yellow,  red,  rose,  or  violet.     The  crystals  of  Ice- 
land spar,  so  called  because  they  were  first  brought  from 
Iceland,  are  transparent,  and  they  exhibit  double  refrac- 
tion— that  is,  objects  seen  through  the  crystal  appeal- 
double.     Satin  spar  has  its  name  from  the  satin  lus- 
tre which  its  beautifully  fibrous  arrangement  presents. 
There  is  a  form  of  carbonate  of  lime,  called  aragonite, 
that  crystallizes  after  a  diiferent  plan  from  that  of  calca- 
reous spar,  and  it  is  much  harder. 

102.  Marble. — This  is  a  granular  limestone,  the  grains 
being  imperfect  crystals  from  their  encroaching  on  each 
other  during  their  formation.     The  finest  varieties  are 
called  statuary  marble,  the  best  coming  from  Carrara,  in 
Italy,  the  island  of  Paros,  and  some  other  localities  in  the 
same  quarter.     The  coarse  kinds  are  the  common  mar- 
bles, which  are  either  white  or  clouded  with  various  col- 
oring substances.     In  some  marbles  there  are  shells  or 
corals,  these  being  composed  of  the  same  mineral  with 
the  marble  itself.    Indeed,  it  is  supposed  by  some  that 
all  marble  and  other  forms  of  carbonate  of  lime  are  made 


OXY-SALTS    AND    HALOID    SALTS.  53 

of  the  shells  and  skeletons  of  animals,  and  that  it  is  by 
the  agency  of  fire  chiefly  that  their  forms  have  been  to 
so  great  an  extent  destroyed,  the  particles  that  composed 
them  having  taken  on  a  crystalline  arrangement  in  the 
marble.  There  is  one  mode  of  arrangement,  differing 
from  the  ordinary  one,  which  I  will  notice  in  passing. 
We  see  it  in  both  marble  and  common  limestone.  It 
gives  to  marble  a  grayish  color,  and  an  appearance  re- 
sembling the  roe  of  a  fish,  from  the  rounded  dots  with 
which  it  is  speckled.  It  is  called  oolitic  marble,  and  the 
limestone  which  is  composed  of  these  round  grains  is 
called  oolite.  This  term  comes  from  the  Greek  word 
don,  egg. 

103.  Stalactites  and  Stalagmites. — In  many  limestone 
caves  the  carbonate  of  lime   accumulates  overhead  in 
shapes  like  icicles,  and  these  are  called  stalactites.     Ac- 
cumulations also  occur  on  the  floor  of  the  cave  similar  in 
form  to  those  which  we  sometimes  see  on  the  ground 
under  dripping  icicles,  and  these  are  called  stalagmites. 
The  resemblance  in  form  in  the  two  cases  is  very  strik- 
ing.    For  the  chemical  explanation  of  these  formations 
I  refer  you  to  §  307,  Part  II.     Sometimes  the  stalactites 
and  stalagmites  meet,  forming  pillars,  and  these  may,  in 
the  course  of  time,  become  very  large,  so  that,  where  the 
roof  is  high,  the  appearance  by  torch-light  is  magnificent. 
In  Weyer's  Cave,  which  is  a  mile  and  a  half  in  extent, 
and  in  some  parts  forty  feet  high,  many  of  the  stalactites 
being  of  a  delicate  white  color,  in  contrast  with  the  blue 
limestone  of  the  walls,  the  scene  is  exceedingly  grand 
and  beautiful. 

104.  Magnesian  Carbonate  of  Lime.  —  This   mineral, 
called  dolomite,  is  composed  of  carbonate  of  lime  and 
carbonate  of  magnesia.     Its  crystals,  which  are  rhombo- 
hedrons,  are  often  curved,  as  seen  in  Fig.  3.     Much  of 
the  coarser  kind  of  white  marble  in  use  for  building  is 
dolomite   in   the   granular   or   imperfectly   crystallized 
form. 


54  MINERALOGY. 

105.  Fluor  Spar, — This  is  a  fluorid  of  calcium,  com- 
posed of  fluorine  (one  of  the  chlorine  family)  and  calci- 
um, which  is  the  metallic  base  of  lime.     Neither  of  these 
elements  is  ever  found  in  nature.     The  crystals  of  fluor 
spar  are  the  cube  and  the  octahedron,  and  their  seconda- 
ries.    Their  colors,  which  are  bright,  are  white,  light 
green,  purple,  and  yellow ;  sometimes  rose-red  and  sky- 
blue.    Fluor  spar  phosphoresces  brightly  when  put  upon 
hot  iron,  giving  out  various  colors.     It  is  an  abundant 
mineral  in  Derbyshire,  England,  and  it  is  therefore  often 
called  Derbyshire  spar.     In  the  massive*  or  granulated 
form  it  is  susceptible  of  a  high  polish,  and  vases,  candle- 
sticks, and  various  articles  of  ornament  are  made  from 
it.     This  mineral  is  present  in  very  small  quantities  in 
the  teeth  and  bones  of  animals ;  and  as  there  must  be  a 
supply  of  it  for  these  structures  from  some  source,  it  is 
found  in  some  plants,  which,  of  course,  have  imbibed  it, 
as  is  the  case  with  silex,  from  the  earth. 

106.  Apatite. — Most  of  this  mineral,  whose  beautiful 
crystals  present  much  variety  of  form,  is  a  compound  of 
phosphoric  acid  and  lime — that  is,  a  phosphate  of  lime. 
But  there  is  intimately  incorporated  with  this  fluor  spar, 
and  a  very  small  quantity  of  the  chlorid  of  calcium. 

107.  Salts  of  Magnesia. — The   sulphate  of  magnesia 
was  noticed  in  §  61.     The  carbonate  appears  like  some 
of  the  varieties  of  carbonate  of  lime  and  dolomite.     Sul- 
phate of  magnesia  (Epsom  salt)  is  often  made  from  it. 
This  is  done  by  means  of  sulphuric  acid,  the  acid  seizing 
the  magnesia  and  uniting  with  it,  the  carbonic  acid  gas, 
of  course,  flying  off  as  it  is  released.     The  hydrate  of 
magnesia  is  a  compound  of  magnesia  and  water,  the  lat- 
ter being  nearly  one  third  of  the  whole.    Borate  of  mag- 

*  The  term  massive  is  applied  to  minerals  that  are  imperfectly 
crystallized — that  is,  having  parts  of  crystals  huddled  together  in  a 
confused  mass.  The  crystals  thus  massed  together  may  be  granular, 
or  fibrous,  or  laminated.  We  have  a  familiar  example  of  the  gran- 
ular in  marble,  and  of  the  laminated  in  slate  rocks. 


OXY-SALTS    AND    HALOID    SALTS.  55 

nesia,  called  boracite,  is  a  compound  of  boracic  acid  and 
magnesia. 

108.  Chlorid  of  Ammonium. — This  was  formerly  sup- 
posed to  be  composed  of  muriatic  acid  and  ammonia, 
but  modern  chemistry  has  discovered  that  it  is  a  com- 
pound of  chlorine  and  ammonium,  a  metal  which  has 
never  yet  been  seen,  but  whose  existence  has  been  satis- 
factorily proved,  as  shown  in  §  230,  Part  II.     The  com- 
mon name  of  this  mineral  is  sal  ammoniac.    It  occurs 
in  the  vicinity  of  volcanoes,  and  is  the  result  of  volcanic 
action. 

109.  Alum. — Common  alum  is  a  double  salt,  a  combi- 
nation of  sulphate  of  alumina  and  sulphate  of  potash. 
But  there  are  other  alums — a  soda  alum,  in  which  there 
is  sulphate  of  soda  in  place  of  the  sulphate  of  potash ;  a 
magnesia  alum,  in  which  there  is  sulphate  of  magnesia ; 
an  iron  alum,  in  which  there  is  sulphate  of  iron ;  an  am- 
monia alum,  in  which  there  is  sulphate  of  ammonia;  and 
a  manganese  alum,  in  which  there  is  sulphate  of  manga- 
nese.   Then  there  is  what  is  called  feather  alum,  which 
is  not  a  double  salt,  but  a  simple  hydrous  sulphate  of 
alumina,  and  therefore  can  not,  strictly  speaking,  be  call- 
ed an  alum.     This  is  more  abundant  in  nature  than  any 
of  the  true  alums.    This  salt,  the  potash  alum  and  the 
iron  alum,  often  impregnate  the  rocks  called  clay  slates, 
and  when  thus  charged  they  are  termed  aluminous  slates 
or  shales.     Alum  is  often  obtained  from  these  rocks  by 
lixiviation. 

110.  Phosphates  of  Alumina. — Wavellite,  a  mineral 
which  is  found  adhering  to  rocks  in  small  hemispheres, 
is  a  phosphate  of  alumina,  having  combined  with  it  a 
small  amount  of  fluorid  of  aluminum.     Turquois,  an 
opaque  greenish-blue  mineral,  much  used  for  ornament, 
is   a  phosphate   of  alumina,  having  combined  with  it 
phosphates  of  copper  and  iron  in  small  quantities.    This 
gem  is  often  imitated,  and  the  counterfeits  are  some- 
times so  good  that  they  can  be  detected  only  by  chemi- 
cal tests. 


56  MINERALOGY. 


CHAPTER  VII. 

EAETHY    MINERALS. 

111.  Composition. — A  large  proportion  of  the  earthy 
minerals  are  silicates  of  the  earths  alumina,  lime,  mag- 
nesia, etc.     These  earths,  as  you  learned  in  Part  II.,  are 
oxyds  of  metals,  and,  united  with  siHca  (that  is,  silicic 
acid),  they  form   salts   called   silicates.     The   different 
kinds  of  glass  are  artificial  silicates,  many  of  them  very 
beautiful,  but  surpassed  greatly  in  beauty  by  many  of 
the  natural  silicates  found  in  the  rocks.     Many  of  these 
silicates  are  very  compound,  the  silica  being  united  with 
several  bases   at  the   same  time.     Some  examples   of 
double  salts  (salts  in  which  one  acid  is  united  with  two 
bases)  were  brought  to  your  notice  in  the  alums,  and 
some  other  salts,  in  the  preceding  chapter.     But  many 
of  the  earthy  minerals  are  much  more  compound  than 
this.    Some  have  not  only  several  bases,  but  more  than 
one  acid.     Thus,  in  that  beautiful  azure-blue  mineral,  la- 
pis lazuli,  we  have  both  silicic  acid  and  sulphuric  acid. 
Some  of  the  earthy  minerals,  on  the  other  hand,  have  a 
very  simple  composition.      Thus  the  splendid  sapphire 
and  common  emery  are  both  the  pure  earth  alumina, 
that  is,  oxyd  of  aluminum ;  and  then  we  have,  as  you 
will  see,  many  varieties  of  quartz,  which  is  pure  silica,  or 
silicic  acid. 

112.  Silica. — This  substance  constitutes  about  45  per 
cent,  of  the  crust  of  the  earth,  some  rocks  being  entirely 
composed  of  it,  but  more  of  them  having  it  in  combina- 
tion or  in  mixture.     In  the  granite  we  have  it  in  both 
these  states,  for  the  quartz  is  pure  silica;  and  while  this 
is  mixed  with  two  other  minerals,  mica  and  feldspar,  in 
these  minerals,  as  you  will  see  in  another  part  of  this 


EAETHY    MINERALS.  57 

chapter,  the  silica  is  in  chemical  combination  with  other 
substances,  forming  silicates.  Silica  is  a  very  hard  sub- 
stance, scratching  glass  readily,  but  inferior  in  hardness 
to  the  diamond.  It  is  insoluble,  and  can  not  be  melted, 
even  in  the  strongest  heat  that  can  be  obtained  by  the 
blow-pipe.  It  appears  in  greater  variety  of  form  and 
color  than  any  other  mineral,  but  its  qualities  are  so 
marked  that  it  is  easily  recognized.  As  it  is  so  abun- 
dant in  the  rocks,  and  yet  hard  and  insoluble,  its  frag- 
ments abound,  most  of  the  pebbles  in  gravel  and  in  the 
common  soil,  most  of  the  sand,  and  much  of  the  hard 
grains  even  in  what  we  call  fertile  earth,  being  silica. 
Of  course,  in  every  case  where  there  is  a  decided  color 
there  is  something  besides  the  silica — that  is,  there  is 
some  coloring  substance.  But  where  the  mineral,  when 
colored,  is  clear  and  transparent,  there  is  so  little  of  a 
foreign  substance,  and  it  is  so  intimately  mixed  or  com- 
bined with  the  silica,  that  it  can  hardly  be  regarded  as 
an  impurity.  But  sometimes,  especially  wrhen  the  min- 
eral is  opaque,  the  impurity  is  palpable — oxyd  of  iron, 
clay,  etc.  Flint  is  one  of  those  opaque  forms.  This, 
which  was  formerly  in  such  wide  use  in  muskets  and  in 
the  common  tinder-boxes,  but  is  now  superseded  by  per- 
cussion caps  and  lucifer  matches,  is  quite  an  abundant 
mineral,  and  is  extensively  used  in  pottery. 

113.  Quartz. — There  are  said  to  be  three  varieties  of 
quartz — the  vitreous,  the  only  one  which  appears  in  crys- 
talline forms,  its  name  coming  from  the  fact  that  its  frac- 
ture is  glassy ;  the  chalcedonic,  generally  translucent, 
with  a  waxy  lustre,  often  exhibiting  several  colors,  gen- 
erally fantastically  arranged  ;  and  the  jaspery,  of  a  dull 
red,  sometimes  yellow  color.  But  in  common  language, 
even  among  mineralogists,  it  is  only  specimens  of  the 
first  variety  that  are  usually  spoken  of  as  quartz ;  and, 
on  the  other  hand,  the  two  terms  silica  and  quartz  are 
often  used  as  being  synonymous.  The  crystals  of  quartz 
are  usually  six-sided  prisms,  terminated  with  six-sided 

C2 


58 


MINERALOGY. 


pyramids,  but  modified  so  as  to  present  much  variety. 
Some  of  the  forms  are  represented  in  Fig.  22.  Some  of 
the  crystals  have  the  pyramidal  terminations  at  both 
ends. 


Fig.  22. 

Nothing  can  be  more  pure  and  transparent  than  clear, 
uncolored,  limpid  quartz.  The  common  name  for  it  is 
rock  crystal.  It  is  said  that  it  was  to  this  mineral  that 
the  ancients  first  gave  the  appellation  of  crystal,  from  its 
resemblance  to  perfectly  clear  ice,  the  Greek  word  for 
ice  being  krustallos.  It  is  often  used  in  jewelry,  and  also 
to  make  lenses  for  optical  instruments.  The  amethyst, 
so  called,  is  a  variety  having  a  purple  or  red  color  from 
the  presence  of  some  oxyd  or  oxyds.  The  rich  purple 
specimens,  so  much  prized  for  jewelry,  derive  their  color 
from  the  oxyd  of  manganese.  Sometimes  the  crystals 
of  quartz  have  a  light  yellow  color,  and  then  are  called 
false  topaz.  Smoky  quartz  appears  with  various  degrees 
of  color.  Crystals  with  the  lighter  shades  are  often  very 
beautiful,  and  are  sometimes  used  in  jewelry.  Sometimes 
quartz  is  filled  with  golden-yellow  spangles  of  mica;  but 
the  artificial  imitations  of  this  mineral,  contrary  to  the 
general  fact  that  nature  excels  art,  transcend  in  beauty 
the  original.  The  colors  of  what  is  called  ferruginous 
quartz,  yellow,  brownish-yellow,  and  red,  are  produced 
from  oxyd  of  iron,  and  hence  its  name,/emm  being  the 
Latin  word  for  iron. 

114.  Chalcedony.  —  This  kind  of  quartz,  as  already 
stated,  does  not  appear  in  crystalline  form,  but  in  spher- 


EARTHY    MINERALS.  59 

ical  arid  nodular  masses.  In  its  various  forms  it  is  used 
for  making  various  articles — cameos,  snuff-boxes,  but- 
tons, marbles,  etc.  The  carnelian,  which  is  so  familiar  to 
you,  is  of  a  bright  red  color,  sometimes  yellow.  There 
is  one  variety  of  an  apple-green  hue,  the  color  being  given 
to  it  by  nickel,  the  metal  found  alloyed  with  iron  in  me- 
teorites (§71).  In  agate  the  colors  are  arranged  either 
irregularly  in  spots  or  clouds,  or  in  regular  layers  around 
a  centre.  Sometimes  the  lines  are  zigzag,  like  the  lines 
of  a  fortification,  and  then  it  is  called  fortification  agate. 
Sometimes  the  oxyd  of  iron  is  arranged  in  this  mineral 
in  moss-like  branches,  giving  it  the  name  of  moss  agate. 
In  the  onyx  the  differently  colored  material  is  in  horizon- 
tal layers,  the  colors  being  commonly  a  light  brown  and. 
a  white.  This  is  the  mineral  which  is  used  for  cameos, 
the  figures  being  cut  in  one  layer,  the  other  layer  furnish- 
ing the  background.  The  variety  of  chalcedony  called 
cat's  eye,  of  a  greenish-gray  color,  has  internal  reflections 
of  light  which  resemble  those  of  the  eye  of  a  cat. 

115.  Opal. — This  mineral  belongs  to  neither  of  the  va- 
rieties of  quartz,  differing  from  them  in  composition  by 
containing  water,  the  water  varying  in  different  speci- 
mens from  5  to  12  per  cent.     The  colors  of  opal  vary 
much  from  the  presence  of  coloring  matters,  which,  espe- 
cially in  the  dark  and  thoroughly  opaque  specimens,  may 
be  regarded  as  impurities.     The  color  of  the  noble  opa\ 
so  highly  prized  as  a  gem,  is  commonly  milky,  and  has  a 
play  of  brilliant  but  delicate  internal  reflections.     In  the 
fire  opal  these  reflections  are  afire-red  iu  color.     Opal 
has  not  as  muoh  hardness  as  quartz. 

116.  Silica  in  Solution. — I  have  stated  that  silica  is  in- 
soluble.    It"  is  ordinarily  so.     But  sometimes  it  is  dis- 
solved in  water  by  means  of  the  potash  in  it,  as  explained 
in  gr  265,  Part  II.     Thus,  in  the  waters  of  the  geysers 
and  some  other  hot  springs,  there  is  silica  in  considerable 
quantity.     Here,  undoubtedly,  heat  aids  the  solution,  but 
it  is  not  its  principal  cause,  for  silica  is  dissolved  in  water 


60  MINERALOGY. 

at  ordinary  temperatures  to  some  extent  in  all  parts  of 
the  globe,  as  is  shown  by  its  deposition  in  grasses  and 
other  plants,  and  in  the  textures  of  animals  also,  especial- 
ly some  of  those  minute  animals  called  infusoria,  as  you 
will  see  in  another  part  of  this  book.  These  deposits 
are  of  course  made  from  solution,  the  solvent  being  the 
sap  in  vegetables  and  the  blood  in  animals. 

117.  Silica  in  two  States. — There  are  two  states,  then, 
in  which  silica  exists,  the  soluble  and  the  insoluble.    Most 
of  it  in  the  world  is  in  the  insoluble  state,  in  the  rocks 
and  pebbles,  and  sand  and  grains  in  the  soil ;  but  some 
of  it  is  changing  continually  from  this  state  into  the  solu- 
ble, and  as  continually  passing  back  again  by  deposition. 
Thus,  by  the  agency  which  I  have  mentioned,  some  of 
the  silica  in  the  soil  (which  came  originally  from  the 
rocks)  is  dissolved  in  the  water,  and  finds  its  way  into 
the  plant  by  the  sap,  where  it  is  deposited  in  the  texture, 
and  when  deposited  it  is  insoluble  again.     If  the  plant 
decay  or  is  burned  the  silica  is  returned  again  to  the 
earth.     The  same  succession  of  changes  we  have  also  in 
relation  to  some  animals.     And  it  is  supposed  that  the 
insoluble  silica  which  we  have  in  chalcedony,  jasper,  etc., 
is  a  deposit  from  the  soluble  state. 

118.  Petrifactions  with  Silica. — When  wood  decays  in 
water  which  contains  considerable  silica  in  solution,  pet- 
rifaction occurs  ;  that  is,  as  the  particles  of  wood  are  re- 
moved in  the  process  of  decay,  particles  of  silica  are  de- 
posited in  their  place.     Of  course  the  silica  is  deposited 
from  a  solution  of  it  that  penetrates  the  wood.     The  ar- 
rangement of  the  wood  is  preserved,  so  that  it  appears 
as  if  the  wood  had  been  turned  into  stone. ,    Some  speci- 
mens are  exceedingly  beautiful  when  sawn  across  what 
was  the  grain  of  the  wood  and  polished. 

119.  Silicates  of  Lime. — These  are  of  so  little  import- 
ance that  I  need  not  describe  them.     The  same  is  true 
of  the  boro-silicates — that  is,  compounds  of  silicic  and  bo- 
racic  acids  with  lime  combined  together  in  one  mineral. 


EARTHY    MINERALS.  61 

120.  Silicates  of  Magnesia. — These  are  of  t^vo  classes, 
the  hydrous  and  the  anhydrous.     In  them  all,  which  are 
numerous,  there  is  not  merely  a  silicate  of  magnesia,  but 
there  are  also  other  oxyds,  some  in  one  and  some  in  an- 
other, as  oxyd  of  iron,  alumina  (oxyd  of  aluminum),  lime 
(oxyd  of  calcium),  the  oxyd  of  manganese,  etc.     These 
additional  oxyds  are  generally  small  in  amount,  but  in 
some  cases  they  make  quite  a  considerable  portion  of  the 
mineral.     I  will  notice  only  the  most  important  of  these 
silicates. 

121.  Talc. — This  is  one  of  the  softest  of  minerals,  being 
easily  cut  with  a  knife.     It  is  commonly  of  a  light  green 
color,  and  has  an  unctuous  feel.     One  of  its  varieties, 
scaly  talc,  is  the  French  chalk  so  familiar  to  us.     Anoth- 
er, the  soapstone  (steatite),  is  found  in  extensive  beds, 
and  is  used  for  many  purposes  —  fireplaces,  linings  for 
stoves,  etc.     It  is,  you  know,  rather  soft,  but  heat  hard- 
ens it.     Powdered  soapstone  is  used  for  lessening  the 
friction  of  machinery. 

122.  Serpentine. — This,  when  so  pure  as*  to  be  called 
precious  serpentine,  is  almost  a  pure  hydrous  silicate  of 
magnesia,  the  only  additional  oxyd  in  it  being  that  of 
iron  in  the  small  quantity  of  0.2  per  cent. — that  is,  -^Jijth 
of  the  wjiole.     When  polished  it  is  a  very  rich-looking 
stone,  the  color  being  green.     Other  varieties  contain 
more  of  the  oxyd  of  iron.     There  are  some  rocks  com- 
posed wholly  of  serpentine,  and  others  that*have  ser- 
pentine mingled  with  other  minerals.     The  verd-antique 
marble  is  granular  limestone  with  serpentine  scattered 
through  it.     Serpentine  was  so  named  from  its  resem- 
blance to  the  skin  of  a  serpent,  being  streaked  or  spotted. 

123.  Chlorite. — This  is  a  dark  green  hydrous  silicate 
of  magnesia,  alumina,  and  iron,  there  being  in  it  17  per 
cent,  of  alumina  and  34  of  magnesia.     In  some  parts  of 
the  earth  there  are  extensive  deposits  of  this  mineral, 
and  also  of  a  slaty  rock,  which  is  called  chlorite  slate, 
because  chlorite  is  its  chief  constituent. 


(32  MINERALOGY. 

124.  Pyroxene. — This  is  a  very  common  mineral,  and 
has  many  varieties.     The  colors  also  are  various,  being 
shades  of  green  from  the  lightest  to  the  darkest.     One 
variety  is  even  white.     One  of  the  additional  oxyds  is 
lime,  which  differs  in  quantity  very  much  in  the  different 
varieties.    Pyroxene  occurs  in  various  rocks — granite, 
limestone,  the  lavas,  etc. 

125.  Hornblende. — This   constitutes  a  large  part  of 
some  rocks,  as  trap  and  some  kinds  of  slates,  giving  to 
them  great  toughness.    Like  pyroxene,  it  contains  lime, 
and  some  of  its  varieties  it  is  difficult  to  distinguish  from 
that  mineral.     Some  of  its  varieties  are  beautiful.     The 
famous  asbestos  is  a  very  remarkable  one,  being  arranged 
in  such  slender  silky  fibres  that  it  may  be  woven  like 
cotton  or  linen  into  cloth.     This  cloth  is  incombustible, 
and,  when  soiled,  can  be  effectually  cleaned  at  once  by 
putting  it  into  the  fire.    The  Greenlanders  use  asbestos 
for  lamp-wicks,  and  in  ancient  times  it  was  used  for  this 
purpose  in  the  temples,  its  incombustibility  being  thought 
to  give  it  a  sacred  character.    Amianthus  is  a  variety  of 
asbestos  which  has  a  satin  lustre.    In  Siberia  and  Spain, 
gloves,  ribbons,  and  purses  are  made  of  it.     The  differ- 
ence between  the  tough  hornblende  that  we  find  in  rocks 
and  this  very  delicate  variety  of  it  is  no  greater  than 
that  between  common  wood  and  the  delicate  varieties 
of  wood  which  we  see  in  the  forms  of  cotton  and  linen, 
and  in  the  textures  of  leaves,  flowers,  etc.,  as  noticed  in 
§  511,  Part  II. 

126.  Alumina. — This  is  an  oxyd  of  aluminum,  a  metal 
which  is  never  found  in  nature,  but  is  obtained  artificial- 
ly from  its  compounds.     Though  this  metal  has  been  lit- 
tle known  till  lately,  it  is  coming  into  considerable  use, 
especially  among  the  French,  on  account  of  qualities 
which  are  noticed  in  §  238,  Part  II.    The  oxyd  alumina 
is  familiar  to  us  in  the  form  of  emery.     This  is  granular. 
But  it  also  appears  in  various  crystalline  forms,  and, 
when  clear,  is  exceeded  in  costliness  only  by  the  dia- 


EARTHY    MINERALS.  63 

mond.  It  is  the  sapphire^  and  is  of  various  colors.  It 
is  only  the  blue  crystals  that  commonly  receive  this 
name,  while  a  red  crystal  of  it  is  called  the  Oriental  ruby, 
and  a  yellow  one  the  Oriental  topaz.  This  mineral  is  in 
hardness  inferior  only  to  the  diamond,  scratching  quartz 
quite  easily.  Alumina  is  the  essential  ingredient  of  all 
clay,  and  is  therefore  very  abundant,  entering  into  the 
composition  of  many  rocks,  and  forming  a  constituent 
more  or  less  of  the  soil.  It  is  calculated  that  aluminum, 
its  base,  is  one  twentieth  part  of  the  crust  of  the  earth. 

127.  Spinel. — This  mineral  is  composed  essentially  of 
alumina  and  magnesia  intimately  combined,  there  being 
small  quantities  in  it  of  other  substances,  as  oxyd  -of 
iron,  silica,  and  chromic  acid.     The  finely-colored  crys- 
tals are  prized  as  gems  in  jewelry,  and  the  red  is  the 
common  ruby,  in  distinction  from  the  Oriental,  which  is 
a  sapphire.    There  are  some  varieties  of  spinel  in  which 
the  oxyd  of  zinc  is  a  prominent  ingredient. 

128.  Silicates  of  Alumina. — There  are  a  few  silicates 
of  alumina  that  have  no  other  substance  in  combination, 
one  of  which  is  named  Sillimanite,  in  honor  of  Professor 
Silliman,  sen.,  of  Yale  College.     But  most  of  the  silicates 
of  this  earth  are  quite  compound,  having  various  oxyds 
and   other   substances    combined   with   them,  as  lime, 
magnesia,  potash,  soda,  oxyd  of  iron,  lithia,  oxyd  of  man- 
ganese, etc.    I  will  notice  a  few  of  those  which  are  most 
prominent  in  interest. 

129.  Feldspar. — This  mineral,  which  is  a  silicate  of 
alumina  and  potash,  is  one  of  the  three  crystalline  con- 
stituents of  granite,  and  its  partially  formed  crystals  are 
easily  distinguished  in  the  coarser  specimens  of  that 
rock.     It  is  not  as  hard  as  quartz,  and  is  more  brittle. 
Its  crystals  are  commonly  four  or  six-sided  prisms,  and 
have  a  pearly  lustre.     Two  of  its  usual  crystals  are  rep- 
resented in  Fig.  23  (p.  64).     The  colors  of  this  mineral 
are  commonly  white,  milk-white,  gray,  and  flesh-colored, 
but  sometimes  the  crystals  are  violet  and  green.    Some- 


64 


MINERALOGY. 


times  feldspar  is  opalescent — 
that  is,  resembling  opal  in  lus- 
tre, and  some  specimens  of 
this  variety  are  used  in  jew- 
elry. Sometimes  it  is  irides- 
cent, from  the  glistening  of 
minute  crystals  of  specular 
.iron  contained  in  it.  Feld- 
spar is  used  largely  in  the 
manufacture  of  porcelain,  the 
clay  which  comes  from  the 
decomposition  of  the  feldspar 
being  called  'kaolin.  Albite,  so  called  from  the  fact  that 
white  is  its  most  common  color,  differs  from  feldspar 
chiefly  in  containing  soda  instead  of  potash.  It  takes 
the  place  of  feldspar  sometimes  in  the  rocks.  It  does 
so  in  granite,  and  albite  granite  differs  from  feldspar 
granite  in  having  a  lighter  color,  owing  to  the  whiteness 
of  the  albite.  Ldbradoriteis  another  mineral  sometimes 
found  in  granite.  It  differs  from  feldspar  and  albite  in 
having  a  large  percentage  of  lime. 

130.  Mica. — This  is  another  of  the  three  constituents 
of  granite.  It  has  chiefly  the  same  substances  in  its 
composition  as  feldspar,  but  there  are  added  small 
amounts  of  oxyd  of  iron,  fluoric  acid,  and  water.  It  has 
many  varieties,  but  that  which  is  so  familiar  to  us  under 
the  common  but  inappropriate  name  of  isinglass  con- 
sists of  extremely  thin  plates,  transparent,  with  a  bright 
lustre,  the  colors  being  white,  yellow,  gray,  brown,  and 
blackish  green.  It  is  very  elastic,  being  unlike  talc  in 
this  respect,  though  resembling  it  in  some  others.  It  is 
used  for  doors  in  lanterns  and  windows  in  ships,  where 
glass,  from  its  brittleness,  is  liable  to  be  broken.  As  it 
bears  heat  well  it  is  used  much  in  stoves.  In  Siberia, 
where  it  is  obtained  in  large  quantities,  it  is  used  in  place 
of  glass.  Plates  of  it  three  feet  square  have  been  brought 
from  that  country,  and  they  have  been  obtained  of  the 


EARTHY    MINERALS.  65 

same  size  in  our  own  country  in  several  localities  in 
New  Hampshire. 

131.  Garnet. — In  this  mineral  there  are  combined  the 
silicates  of  alumina,  lime,  iron,  and  manganese,  and  the 
various  colors  of  the  different  specimens  generally  come 
from  the  difference  in  proportions  of  these  ingredients. 
The  most  common  color  is  deep  red.     In  an  emerald- 
green  variety  the  color  is  caused  by  oxyd  of  the  metal 
chromium.     Clear  garnets  of  a  deep  red  color  are  highly 
prized  in  jewelry. 

132.  Tourmaline. — The  usual  form  of  the  crystals  of 
this  mineral  is  a  prism  terminating  in  a  low  pyramid. 
They  are  commonly  long,  and  the  sides  are  apt  to  be  fur- 
rowed.    The  most  common  colors  are  black,  blue-black, 
and  dark  brown ;  but,  besides  these,  there  are  wide  vari- 
eties, as  bright  and  pale  red,  grass-green,  yellow,  etc., 
even  to  white.     Though  alumina  is  the  chief  base  in  all 
the  varieties,  the  differences  in  the  composition  of  some 
of  the  varieties  are  considerable.    For  example,  in  a  black 
variety  there  was  found  to  be  24  per  cent,  of  oxyd  of  iron, 
while  in  a  red  variety  there  was  no  iron  at  all,  but  5  per 
cent,  of  the  peroxyd  of  manganese,  a  frequent  cause  of 
this  color  in  minerals.     Some  red  and  yellow  tourmalins 
are  of  great  value  as  gems.     A  Siberian  tourmaline  of 
the  red  variety,  now  in  the  British  Museum,  is  considered 
to  be  worth  £500. 

133.  Topaz. — This  is  said  to  be  a  silicate  combined 
with  a  fluorid.     If  so,  it  must  be  a  combination  of  sili- 
cate of  alumina  with  fluorid  of  the  metal  aluminum,  for 
there  can  be  no  such  thing  as  a  fluorid  of  alumina  any 
more  than  there  can  be  a  chlorid  of  soda.     In  explana- 
tion of  this  I  refer  you  to  §  352,  Part  II.     The  clear  crys- 
tals of  topaz  are  used  in  jewelry,  and  it  is  a  curious  fact 
that  the  color  can  be  altered  for  this  purpose  by  exposure 
to  heat.     The  Brazilian  topaz  can  be  thus  made  so  to  re- 
semble the  real  rose-red  ruby  that  it  can  not  be  distin- 
guished from  it  except  by  an  electrical  test.     When  the 


66  MINERALOGY. 

most  clear,  pellucid  pebbles  of  topaz  are  cut  with  facets 
and  set,  they  appear  by  daylight  precisely  like  diamonds. 

134.  Lapis  Lazuli. — In  this  beautiful  azure-blue  miner- 
al we  have  a  compound  of  silica,  alumina,  soda,  lime,  iron, 
sulphuric  acid,  sulphur,  chlorine,  and  water.     It  is  plain 
that  the  silicic  acid  and  the  sulphuric  acid  must  form  with 
some  of  these  oxyds  a  silicate  and  a  sulphate,  which  are 
intimately  combined  together,  but  how  some  of  these 
substances  are  combined  we  know  not.     The  color  is  at- 
tributed to  sulphuret  of  sodium.     There  are  some  speci- 
mens of  this  mineral  whose  composition  differs  somewhat 
from  that  given  above. 

135.  Beryls  and  Emeralds. — A  beryl  is  a  silicate  of 
alumina  and  glucina,  while  an  emerald  is  the  same,  col- 
ored with  oxyd  of  chromium  to  the  amount  ofless  than 
one  per  cent.     The  color  is  mostly  green — pale  in  the 
beryl,  but  decided  and  rich  in  the  emerald.    The  best 
emeralds  are  brought  from  Granada,  where  they  are 
found  in  dolomite  (§  104).     One,  weighing  six  ounces, 
cost  the  owner,  Mr.  Hope,  of  London,  £500.     Emeralds 
of  larger  size,  but  of  less  beauty,  are  obtained  in  Siberia. 
One  in  the  royal  collection  of  Russia  measures  four  and  a 
half  inches  by  twelve.     The  finest  beryls  come  from  Si- 
beria, Hindostan,  and  Brazil.     Some  beryls  of  very  great 
size  have  been  obtained  in  this  country,  but  they  are 
seldom  transparent.     A  hexagonal  prism  was  found  in 
Grafton,  New  Hampshire,  of  such  enormous  size  that  it 
weighed  2900  pounds.     It  is  four  feet  in  length.     The 
chrysoberyl  is  a  combination  of  alumina  and  glucina, 
sometimes  with  a  little  iron.     The  color  is  indicated  by 
the  name,  which  comes  from  two  Greek  words,  chrysos, 
yellow,  and  beryllos,  beryl. 

136.  Zircon. — This  mineral,  which  is  a  silicate  of  the 
earth  zirconia,  has  various  colors.     The  clear  crystals  are 
in  common  use  in  jewelry.     "When  they  are  red  they  are 
called  hyacinths.     This  variety  has  some  resemblance  to 
the  red  spinel.     Zircon  is  used  in  jeweling  watches. 


ROCKS.  67 


CHAPTER  VIII. 

ROCKS. 

137.  Connection  of  Mineralogy  with  Geology. — In  this 
chapter  we  shall  pass  over  ground  that  connects  miner- 
alogy with  geology.     We  have  looked  at  minerals  in  de- 
tail and  in  their  separate  condition,  merely  alluding  to 
them  occasionally  as  being  masses,  but  now  we  are  defi- 
nitely to  consider  these  masses  preparatory  to  a  view  of 
them  as  a  whole,  making  up  the  crust  of  the  earth.     It 
is  such  a  view  that  constitutes  Geology,  the  term  being 
derived  from  two  Greek  words,  ge^  earth,  and  logos^  dis- 
course. 

138.  Definition  of  Rock. — The  word  rock,  in  common 
language,  is  applied  only  to  such  mineral  aggregates  of 
considerable  size  as  are  solid ;  but  the  geologist  gives  it 
a  wider  meaning.     He  speaks  of  all  such  aggregates  as 
rocks,  whether  they  are  solid  or  made  up  of  loose  mate- 
rial.   Thus  the  clay  slate,  and  the  strata  of  clay  mud, 
which,  by  long-continued  pressure,  or  this  and  heat  to- 
gether, might   ultimately  become   clay   slate,  are  both 
equally  regarded  as  rock.     The  same  may  be  said  of 
sandstones  and  deposits  of  sand.     The  geologist,  how- 
ever, often  uses  the  word  rock  in  its  ordinary  sense,  the 
context  showing  in  which  sense  he  does  use  it. 

139.  Elementary  Substances  in  the  Rocks. — There  are 
between  sixty  and  seventy  elements,  but  only  nine  of 
them  enter  to  any  great  extent  into  the  composition  of 
the  rocks,  viz.,  oxygen,  silicon,  aluminum,  calcium,  mag- 
nesium, potassium,  sodium,  iron,  and  carbon.     Of  these 
only  one,  oxygen,  is  a  gas,  but  that  is  so  abundant  that 
it  is  supposed  to  constitute  nearly  or  quite  one  half  of 
all  the  ponderable  matter  in  the  globe.     These  elements, 


68  GEOLOGY. 

it  is  stated  by  Dana,  make  up  ^^ths  of  the  rocks  as  a 
whole.  But  there  are  some  other  elements  which  enter 
into  the  composition  of  some  rocks.  Sulphur  exists  in 
sulphate  of  lime  or  gypsum,  which  in  some  parts  of  the 
earth  occurs  as  a  rock  in  beds  of  considerable  extent. 
This  is  the  only  compound  containing  sulphur  of  which 
any  rocks  are  made.  Sulphurets,  as  you  saw  in  Chapter 
IV.,  are  abundant,  but  they  are  only  ores  in  rocks,  and 
do  not  enter  into  their  composition.  Hydrogen  is  an- 
other element  that  is  present  in  some  rocks.  It  is  pres- 
ent in  the  water,  which  is,  as  you  have  seen,  a  component 
of  hydrous  minerals,  and  some  of  these,  as  gypsum  and 
serpentine,  form  rocks.  The  amount  of  water  in  gypsum 
is  21  per  cent. 

140.  Compounds  in  the  Rocks. — The  elements  of  which 
I  have  spoken  do  not  form  rocks  as  elements,  but  as  com- 
pounds.    Thus  oxygen  forms  with  silicon  a  compound, 
silica  or  silicic  acid ;  and  this  silica  constitutes  rock  of 
itself  (quartz  rock) ;  or  makes  a  part  of  a  mixture  of  rock, 
as  in  the  quartz  of  granite ;  or,  uniting  with  some  oxyds, 
makes  silicates,  as  in  the  feldspar  and  mica  of  granite,  in 
serpentine,  in  chlorite,  etc.     The  most  important  of  the 
compounds  which  compose  the  rocks  of  the  globe  are 
silica,  carbonate  of  lime,  and  various  silicates,  viz.,  feld- 
spar, mica,  hornblende,  and  pyroxene.    Besides  these,  the 
only  minerals  that  have  any  large  share  in  making  up 
the  earth's  crust  are  chlorite,  serpentine,  talc,  gypsum, 
and  coal.     All  these  minerals  have  been  sufficiently  de- 
scribed in  previous  chapters. 

141.  Crystalline  and  Uncrystalline  Rocks. — It  is  plain 
that  marble  is  crystalline,  although  none  of  the  individ- 
ual crystals,  as  they  were  crowded  together  in  their  for- 
mation, was  completed.     The  glistening  is  occasioned 
by  the  small  portions  of  the  faces  of  the  crystals  which 
reflect  the  light.     The  same  incomplete  crystalline  struc- 
ture is  seen  in  the  three  minerals  that  compose  granite, 
as  we  look  at  a  fractured  face  of  that  rock.     But  sand- 


ROCKS.  69 

stones  were  evidently  formed  by  a  different  process. 
Here  we  have  grains  mechanically  mixed,  as  in  a  layer 
of  sand  on  a  sea-shore,  and  then  in  some  way  becoming 
solid  rock.  The  grains  themselves  may  have  been  form- 
ed at  the  outset  when  they  were  a  part  of  some  other 
rock  by  a  crystallizing  process ;  but  after  the  original 
rock  became  broken  and  worn  in  one  way  and  another 
into  these  grains,  they  became  arranged  by  the  agency 
of  water  in  layers,  and  changed  into  solid  rock  by  means 
which  we  shall  hereafter  consider. 

142.  Rocks  Composed  of  a  Single  Mineral.  —  Rocks 
sometimes  are  composed  of  one  mineral  alone.    Pure 
limestone,  in  its  three  varieties  of  common  limestone, 
chalk,  and  marble,  is  of  this  character,  being  simple  car- 
bonate of  lime.     Sometimes,  though  a  rock  may  be  a 
single  mineral  throughout,  that  mineral  may  not  be  sim- 
ple in  its  composition.    Thus  the  rock  called  dolomite 
is  a  magnesian  carbonate  of  lime,  or,  in  other  words, 
carbonate  of  lime  and  carbonate  of  magnesia  intimately 
combined,  so  as  to  make  one  mineral.     Other  examples 
of  rocks  composed  of  a  single  mineral  are  quartz  rock, 
gypsum  (sulphate  of  lime),  serpentine,  etc. 

143.  Rocks  Composed   of  more  than  one  Mineral. — 
Most  rocks  are  constituted  by  a  mixture  of  different 
minerals.     Granite  is  a  familiar  example,  being  a  mix- 
ture of  quartz,  feldspar,  and  mica.    Sometimes  the  ingre- 
dients are  so  finely  mingled  that,  different  from  granite, 
the  composite  minerals  can  not  be  at  all  distinguished. 
Pudding-stones  are  aggregates  or  conglomerates  of  peb- 
bles, united  by  some  cementing  mineral,  most  commonly 
silica,  or  oxyd  of  iron,  or  carbonate  of  lime.     The  peb- 
bles may  be  of  one  kind  or  of  different  kinds,  and  they 
vary  much  in  size.     When  the   conglomerate  contains 
angular  pieces  instead  of  rounded  pebbles,  it  is  called 
breccia.     Usually  the  pebbles  or  pieces  are  granite,  or 
quartz,  or  carbonate  of  lime,  and  the  conglomerate  is  ac- 
cordingly said  to  be  respectively  granitic,  quartzose,  or 


70  GEOLOGY. 

calcareous,  this  latter  term  being  commonly  applied  to 
all  compositions  in  which  there  is  limestone. 

144.  Stratified  and  Unstratified  Rocks. — It  is  manifest 
to  the  most  superficial  observer  that  some  rocks  are  in 
layers  or  strata,  while  others  have  a  very  different  ar- 
rangement.    A  full  consideration  of  the  modes  of  con- 
struction of  the  different  forms  of  rock  belongs  to  an- 
other part  of  this  book.     Suffice  it  to  say  now  that  the 
materials  of  the  stratified  rocks  were  assorted  and  laid 
down  by  water,  and  then  by  some  means  became  solidi- 
fied, while  the  unstratified  were  made  under  the  influ- 
ence of  strong  heat. 

145.  Silicious,  Argillaceous,  and  Calcareous  Rocks. — 
Stratified  rocks  are  divided  into  three  classes,  according 
to  their  composition.     The  first  class  is  the  silicious  or- 
arenaceous.    This  is  the  sandy  division,  called  arenaceous 
from  arena,  the  Latin  word  for  sand,  and  silicious,  be- 
cause the  grains  of  which  the  rock  is  composed  are 
silica,  or  silex,  as  it  is  commonly  called.     The  second 
class,  the  argillaceous,  are  made  of  clay,  which  is  a  mix- 
ture of  silex  and  alumina,  commonly  in  the  proportion 
of  about  three  of  the  former  to  one  of  the  latter.    The 
name  comes  from  argil,  a  term  applied  technically  to 
alumina,  and  probably  to  clay.     It  is  a  characteristic  of 
rocks  of  this  class  that  they  give  out  a  peculiar  earthy 
odor  when  breathed  upon,  which  is  not  owing  to  the 
presence  of  alumina  simply,  but  to  a  combination  of  this 
with  some  oxyd  of  iron.     Calcareous  rocks  are  those 
which  are  composed  of  lime  and  carbonic  acid.     These 
three  classes  of  rocks  are  seldom  found  pure,  but  they 
run  into  each  other.     For  example,  there  are  sandstones 
which  are  not  wholly  silicious,  the  silicious  grains  being 
united  together  by  carbonate  of  lime.     Whether  any  si- 
licious or  argillaceous  rock  has  the  carbonate  of  lime  in 
it  can  at  once  be  ascertained  by  the  application  of  sul- 
phuric acid  (§  60.) 

I  pass  now  to  consider  some  of  the  individual  rocks. 


BOCKS. 


71 


146.  Granite. — Ordinary  granite  is  a  mixture  of  quartz 
or  silex,  mica,  and  feldspar.  There  is  great  variety  in 
this  rock,  according  to  the  varying  proportions  of  these 
minerals,  and  each  variety  is  termed  feldspathic,  mica- 
ceous, or  quartzose,  as  one  or  the  other  mineral  predom- 
inates. There  are  other  variations  also.  Sometimes 
hornblende  is  present  in  place  of  mica,  and  then  the  rock 
is  called  syenite.  This  is  even  more  durable  than  com- 
mon granite.  Its  name  comes  from  Syene,  in  Upper 
Egypt,  the  locality  from  which  most  of  the  stones  of  the 
ancient  Egyptian  monuments  were  obtained.  These  are 
not,  however,  true  syenite,  but  a  red  granite,  containing 
considerable  dark-colored  mica.  The  rock  of  Mount  Si- 
nai is  real  syenite.  When  albite  is  in  the  place  of  feld- 
spar, the  rock  is  called  albite  granite  (§  129).  When 
talc  replaces  it,  it  is  called protogine.  When  the  feldspar 
appears  in  the  granite  in  large  crystals,  it  is  called  por- 
phyritic  granite.  There  is  a  peculiarity  in  the  crystal- 
line arrangement  of  one  kind  of  granite  which  produces 
figures  over  its  surface  like  small  Oriental  characters, 
and  hence  this  variety  is  styled  graphic  granite.  In  Fig. 
25  is  given  the  surface  of  a  slab  of  this  granite,  and  in 
Fig.  24  its  end.  The  colors  of  granite  vary  much,  but  it 


Fig.  25. 

is  usually  grayish,  white,  or  flesh-colored. 
Rocks  of  the  granite  family  are  widely  disseminated  in 
the  earth,  often  forming  extensive  mountain  ranges.  In 
some  parts  of  the  Andes  granite  rises  to  the  height  of 
12,000  feet.  In  the  Alps,  the  Aiguille  de  Dree  is  a  solid 
spire  of  granite  4000  feet  high.  There  is  much  granite 


72  GEOLOGY. 

, 

of  different  kinds  in  New  England,  Massachusetts  being 
truly  the  granite  state  of  the  Union,  though  New  Hamp- 
shire is  generally  called  so. 

147.  Uses  of  Granite. — Granite,  on  account  of  its  dura- 
bility, is  one  of  the  most  valuable  materials  for  buildings 
and  monuments.     It  was  much  used  by  the  ancients,  and 
there  are  obelisks  of  granite  in  Egypt  that  have  been  ex- 
posed to  the  weather  for  three  thousand  years,  and  yet 
are  in  good  condition.     Commonly,  the  finer  is  the  tex- 
ture of  granite,  the  more  durable  is  it.     Syenite,  which  is 
so  durable,  is  of  a  fine  texture,  but  it  owes  its  durability 
partly  to  the  toughness  which  hornblende  imparts  (§ 
125).     If  there  be  pyrites  or  any  other  ore  of  iron  dis- 
seminated through  the  rock,  it  impairs  its  value  essen- 
tially, because  by  decomposition  rust  is  produced,  defac- 
ing and  often  crumbling  the  stone.    Some  granites,  which 
present  a  good  appearance  on  being  taken  out  of  the 
quarry,  very  soon  crumble  on  continued  exposure  to  the 
air  without  any  obvious  cause.     This  shows  the  neces- 
sity of  proper  examination  in  selecting  granite  for  build- 
ing.    As  feldspar  contains  a  large  proportion  of  alumina, 
feldspathic  granite  is  much  used  in  obtaining  the  kaolin 
for  making  porcelain. 

148.  Gneiss. — This  is  a  rock  which  has  precisely  the 
same  mixture  of  minerals  in  it  that  granite  has,  but  the 
arrangement  is  different.     It  is  a  stratified  rock.     It  is 
foliated ;  that  is,  it  is  in  leaves,  and  is  split  easily  in  dif- 
ferent thicknesses,  varying  from  a  few  inches  to  a  foot 
or  more.     This  cleavage  occurs  where  the  mica  is  most 
abundant.     When  it  cleaves  in  thin  slabs  it  is  used  for 
flagging,  but  when  it  can  be  got  out  in  thick  blocks  it 
is  used  for  building.     Some  of  the  buildings  of  Amherst 
College  are  constructed  of  this  material,  and  present  a 
fine  appearance.     There  are  many  quarries  of  it  in  Mas- 
sachusetts, and  some  in  Connecticut. 

149.  Slates,  Shales,  and  Schists. — These  terms  are  oft- 
en used  as  being  synonymous ;  but  when  they  are  used 


as  having  different  meanings,  the  disuuUlilOlJS  are  these: 
Slate  is  the  term  used  when  the  rock  splits  into  thin 
laminae,  and  when  the  word  is  used  alone  it  means  clay 
slate.  But  there  are  mica  slates,  hornblende  slates,  etc. 
The  word  shale  is  used  when  the  rock,  though  slaty,  is 
more  brittle  than  slate,  and  so  crumbles  readily.  Schist 
includes  rocks  so  coarse  that  it  would  not  be  proper  to 
call  them  slates  or  shales.  It  comes  from  the  Greek  word 
schistoS)  divided  or  split. 

Mica  slate,  or  schist  (for  it  is  called  by  both  names),  has 
the  same  ingredients  with  gneiss,  but  has  less  of  feldspar 
and  more  of  mica  in  it.  The  scales  of  mica  give  a  glis- 
tening appearance  to  the  surface  of  the  slabs,  which  are 
used  for  flag-stones,  hearth-stones,  and  door-steps.  Fur- 
naces are  sometimes  lined  with  them.  Scythe-stones  are 
made  out  of  varieties  that  have  a  fine  grain. 

Hornblende  slate,  or  schist,  is  more  durable  than  mica 
slate,  from  the  toughness  which  the  hornblende  gives  it 
(§  125),  and  is  therefore  very  valuable  for  flagging. 

Talcose  slate,  or  schist,  is  brittle,  but  is  used  for  fire- 
stones. 

.  Clay  slate  has  about  the  same  composition  with  mica 
slate,  but  the  ingredients  are  so  finely  mixed  that  they 
can  not  be  distinguished  from  each  other.  The  colors 
are  commonly  bluish,  greenish,  gray,  or  reddish.  Slate 
is  used  for  roofing,  and  for  making  drawing-slates,  pen- 
cils, etc. 

150.  Quartz  Rock. — This  is  composed  of  quartz,  either 
in  the  granular  or  arenaceous  (sandy)  form.  There  are 
varieties  which  result  from  the  admixture  of  other  sub- 
stances, as  mica,  feldspar,  etc.  In  these  varieties  there  is 
regular  stratification,  especially  in  the  micaceous,  which 
often  cleaves  into  slabs,  like  gneiss  and  mica  slate ;  but 
when  the  rock  is  unmixed  granular  quartz  there  is  no  ob- 
vious stratification.  Quartz  rock  is  used  for  flag-stones, 
hearth-stones,  and  fire-stones,  and  in  the  form  of  cobble- 
stones for  paving.  The  fine  sand  into  which  this  rock 

D 


4  GEOLOGY. 

sometimes  crumbles  is  employed  in  making  glass,  and  in 
sawing  and  polishing  marble.  The  sand  of  our  sand- 
paper comes  from  this  source.  The  buhrstone^  which  is 
made  into  mill-stones,  is  quartz  rock  that  is  full  of  little 
spaces  or  cells,  these  making  the  surface  rough  with  sharp 
minute  edges  crossing  each  other  in  every  direction. 

151.  Sandstones. — These  usually  consist  mostly  of  sili- 
cious  sand,  some  of  the  varieties  of  quartz  rock  approach- 
ing very  nearly  to  them  in  character.     Sometimes  there 
is  much  clay  in  their  composition,  and  then  the  rock  is 
called  an  argillaceous  sandstone.     Sometimes  there  are 
silicious  pebbles  imbedded  in  the  rock,  making  it  in  part 
a  pudding-stone,  and  in  that  case,  if  the  rock  be  very 
hard,  it  is  called  a  grit  rock  or  mill-stone  grit.     Some 
sandstones  that  readily  split  into  comparatively  thin  lay- 
ers are  much  used  for  flagging-stones.     Sandstones  have 
dull  colors  of  various  kinds,  from  white,  through  grades 
of  yellow,  red,  and  brown,  even  to  black,  these  being 
caused,  of  course,  by  various  substances  combined  with 
the  silex  or  quartz.     When  sandstone  has  a  fine,  even 
grain,  it  is  a  very  beautiful  building  material.     More  cau- 
tion is  necessary  in  selecting  sandstone  for  building  than 
granite,  because  varying  circumstances  of  exposure  to* 
air,  moisture,  and  heat  have  so  much  influence  upon  it. 
The  sandstone  obtained  chiefly  from  New  Jersey  and  va- 
rious localities  in  the  valley  of  the  Connecticut,  now  so 
much  used  in  almost  all  parts  of  the  country  to  which  it 
can  be  carried  by  water,  is  generally  an  excellent  mate- 
rial.    That  used  in  building  the  Capitol  at  Washington, 
which  came  from  the  Potomac,  is,  unfortunately,  an  infe- 
rior article. 

152.  Trappean  Rocks. — This  appellation  is  given  to 
certain  rocks  which  have  such  resemblance  to  each  other 
as  makes  it  proper  to  group  them  together.     The  term 
trap  comes  from  a  Swedish  word  meaning  stair,  the  rocks 
of  this  class  often  presenting  to  the  eye  an  appearance 
like  steps.    The  term  greenstone  is  applied  to  the  com- 


ROCKS.  Y5 

pact  rocks  of  this  class  in  which  hornblende  is  largely 
present,  and  imparts  a  green  color.  Basalt  is  much  like 
greenstone,  but  is  black  or  grayish-black.  It  contains 
small  grains  of  a  silicate  of  magnesia  and  iron,  called  ol- 
ivine,  from  its  olive-green  color.  Trachyte  is  a  grayish- 
white  rock  composed  of  feldspar,  hornblende,  and  mica. 
Clinkstone  is  a  grayish-blue  feldspathic  rock,  which  bears 
this  name  because  it  rings  like  iron  when  struck  with  a 
hammer.  The  term porp hyry  is  used  in  reference  to  the 
structure  of  rocks  rather  than  their  composition.  It  is 
applied  to  any  feldspathic  rock  that  has  crystals  dissem- 
inated through  it.  It  is  called  greenstone  porphyry,  ba- 
saltic porphyry,  etc.,  according  to  the  material  which 
makes  up  the  body  of  the  rock,  or,  as  it  is  commonly  ex- 
pressed, the  base  of  the  rock.  What  the  ancients  called 
porphyry  is  a  rock  having  a  base  of  compact  feldspar, 
with  imbedded  crystals  of  feldspar  of  various  sizes,  from 
a  very  small  size  up  to  a  length  of  three  fourths  of  an 
inch.  The  name  amygdaloid  refers  also  to  structure. 
It  comes  from  two  Greek  words,  amygdale,  almond,  and 
eidos,  like,  and  is  applied  to  any  rock  of  the  trap  family 
that  has  in  it  rounded  cavities  filled  with  some  mineral 
different  from  the  base  of  the  rock.  The  appearance  is 
as  if  the  rock  was  once  in  a  pasty  state,  and,  when  so, 
these  rounded  bodies  were  mixed  up  with  it  like  almonds 
in  cake. 

153.  Tendency  of  Trappean  Rocks  to  the  Columnar 
Form. — In  some  cases  the  tendency  of  rocks  of  the  trap 
family  to  take  on  a  columnar  arrangement  is  shown  in 
the  most  decided  manner.  One  of  the  most  noted  ex- 
amples is  in  FingaPs  Cave,  on  the  island  of  Staffa,  rep- 
resented in  Fig.  26  (p.  76).  Another  is  the  Giant's  Cause- 
way, in  Ireland.  The  columns  vary  from  20  to  200  feet  in 
height,  and  are  jointed,  presenting,  therefore,  an  appear- 
ance as  if  they  had  been  built  up  by  putting  one  pentag- 
onal or  five-sided  stone  upon  another.  Where  the  sea 
has  dashed  against  them  they  are  more  or  less  worn 


76 


GEOLOGY. 


Fig.  26. 

away  above,  and  below  extend  to  unknown  depths  be- 
low the  water.  Looking  like  ruins  of  some  ancient 
work  too  great  for  man,  it  is  not  strange  that  popular 
tradition  has  connected  with  them  the  agency  of  giants. 
In  most  cases  the  tendency  is  only  partially  exhibited, 
as,  for  instance,  in  East  and  West  Rock,  at  New  Haven. 
The  columns  are  prisms,  having  from  three  to  eight 
sides,  commonly  five  or  six,  and 
they  are  generally  divided  into 
blocks  by  joints,  as  seen  in 
Fig.  27.  Each  block  is  usually 
concave  on  its  upper  part,  hav- 
ing the  lower  convex  end  of 
the  block  above  fitting  into  it. 
___ Commonly  the  columns  stand 

Fig.  27. 

upright,  but  sometimes 
they  are  horizontal,  as  in 
Fig.  28,  representing  a  ba- 
saltic dike  in  North  Caro- 
lina. The  appearance  in  this  case  is  that  of  a  wall  built 
as  a  fortification.  Sometimes  the  columns  are  in  the  po- 
sition represented  in  Fig.  29.  Sometimes  the  columnar 
and  massive  forms  are  conjoined,  as  seen  in  this  figure. 
A  remarkable  example  both  of  this  position  of  columns 


Fig.  28. 


EOCKS.  77 

and  their  union  with  the  massive  rock  is 
to  be  seen  on  Mount  Holyoke,  in  Massa- 
chusetts, in  Titan's  Piazza,  so  called  be- 
cause there  is  a  group  of  columns  of 
greenstone  pointing  downward  from  the 
overhanging  rock  above. 

The  manner  in  which  rocks  of  this 
family  are  formed  will  be  considered  in 
another  part  of  this  book. 

154.  Trappean  Rocks  in  this  Country. — 
Beginning  at  the  north,  there  is  a  belt  of  trap  extending 
130  miles  along  the  Bay  of  Fundy,  where  the  violence 
of  the  waves  has  exposed  to  view  magnificent  groups  of 
columns  three  and  four  hundred  feet  in  height.  In  the 
neighborhood  of  Boston,  at  Nahant,  Lynn,  etc.,  there  are 
ridges,  some  of  them  rising  to  the  height  of  500  feet. 
A  range  beginning  at  East  and  West  Rock,  New  Ha- 
ven, extends  up  the  valley  of  the  Connecticut  almost  to 
Vermont,  including  Mounts  Tom  and  Holyoke,  which 
rise  to  a  height  of  over  a  thousand  feet.  The  noted 
Palisades,  on  the  Hudson,  are  greenstone.  Three  ridges 
of  trap  extend  through  the  State  of  New-Jersey,  and 
trap  rocks  are  found  in  beds  and  elevations  as  far  south 
as  North  Carolina.  But  it  is  west  of  the  Rocky  Mount- 
ains that  trap  most  abounds  and  reaches  the  highest  ele- 
vations. Columbia  River  has  on  each  side  of  it  mount- 
ains of  trap,  in  some  cases  even  a  thousand  feet  in  height. 
The  appearance  of  the  columns  is  seen  in  Fig.  30,  p.  78. 

155.  Lavas. — The  materials  thrown  out  from  volca- 
noes become,  as  they  solidify,  what  are  called  lava?^  The 
various  kinds  differ  in  structure  and  composition,  and, 
of  course,  in  color.  There  are  two  classes  of  lavas — the 
light  colored,  in  which  feldspar  is  the  chief  constituent, 
and  the  dark  colored,  or  basaltic,  which  are  grayish- 
blue,  even  to  black.  The  structure  of  lavas  depends 
upon  circumstances.  That  which  cools  under  pressure, 
and  while  shut  in  from  the  atmosphere,  is  compact ;  but 


78 


GEOLOGY. 


Fig.  30. 

that  which  is  at  the  surface,  owing  to  rapidity  of  cool- 
ing and  the  action  of  the  air,  is  porous,  and  has  the  name 
of  scoria.  What  is  called  pumice,  it  is  supposed,  was 
cooled  by  being  thrown  into  water.  Though  its  mineral 
constitution  is  the  same  with  the  hard,  compact  lava,  it 
will  float  on  water  from  its  great  porousness.  It  is  used 
for  polishing  various  substances,  as  wood,  ivory,  mar- 
ble, glass,  parchment,  etc.  Obsidian  and  pitchstone  are 
vitreous  or  glassy  lavas,  the  former  resembling  glass 
more  than  the  latter,  which  receives  its  name  from  its 
pitCivJ  lustre.  The  lavas  are  very  much  like  the  rocks 
of  the  trap  family,  a  fact  which  is  of  much  significance 
in  relation  to  the  formation  of  the  latter,  as  you  will  sec 
in  a  future  stage  of  our  investigation. 

There  are  other  rocks — limestone,  serpentine,  etc.; 
but  these  I  have  spoken  of  sufficiently  before. 


THE   EARTH    AS    IT    IS.  7  9 


CHAPTER  IX. 

THE   EARTH   AS   IT   IS. 

156.  The  Earth  as  a  Whole. — The  earth  is  a  ball  near- 
ly round,  composed  of  solid,  liquid,  and  gaseous  substan- 
ces, the  gaseous  occupying  the  interstices  of  both  solids 
and  liquids,  there  being  also  a  gaseous  envelope  around 
the  earth  of  about  fifty  miles  in  thickness.  The  most 
abundant  liquid  is  water,  which  fills  up  all  the  cavities 
on  the  earth's  surface.  If  the  solid  part  of  the  earth 
were  uniform  instead  of  having  its  present  diversified 
condition,  it  would  every  where  be  covered  with  water, 
the  atmosphere  remaining,  as  now,  outside  of  the  liquid 
envelope.  The  earth,  as  a  whole,  has  been  found,  by  vari- 
ous observations  and  calculations,  to  be  between  five  and 
six  times  the  weight  of  water,  and  about  two  and  a  half 
times  as  heavy  as  the  average  of  common  rocks.  This 
great  weight  of  the  earth  is  owing  to  the  pressure  to 
which  its  internal  parts  are  subjected  from  the  influence 
of  gravitation.  Every  thing  is  attracted  toward  the 
centre,  and  therefore  any  internal  portion  of  the  globe  is 
pressed  toward  this  centre  by  the  weight  of  all  which  is 
outside  of  it.  It  is  just  as  the  lower  portions  of  the  air 
— that  is,  those  which  are  close  to  the  earth — are  con- 
densed by  the  pressure  of  those  portions  outside  of  them 
through  gravitation,  as  illustrated  in  §  152,  Part  I.  It 
has  been  calculated  that  at  the  depth  of  34  miles  in  the 
earth  air  would  be  so  condensed  that  it  would  be  as 
heavy  as  water,  and  at  the  depth  of  362  miles  water 
would  be  so  condensed  that  it  would  be  as  heavy  as 
mercury,  although  here  upon  the  surface  of  the  earth 
water  is  so  little  compressed  by  the  strongest  pressure 
man  can  bring  to  bear  upon  it  that  it  is  regarded  practi- 


.80 


GEOLOGY. 


cally  as  incompressible.  It  is  also  calculated  that  steel 
at  the  centre  of  the  globe  would  be  compressed  into  a 
fourth  of  its  bulk,  and  most  rocks  into  an  eighth  of  their 
bulk. 

157.  Form  of  the  Earth. — I  have  said  that  the  earth  is 
nearly  round.  Its  deviation  from  a  perfectly  spherical 
shape  is  very  slight — that  is,  compared  with  its  whole 
bulk.  Though  it  bulges  out  at  the  equator  13^  niiles, 
this,  in  a  ball  eight  thousand  miles  in  diameter,  is  but  a 
small  matter.  This  can  be  shown  by  the  diagram,  Fig. 
31.  Let  the  curved  line  PEPE  represent  the  circum- 


Fig.  31. 


ference  of  the  earth  as  it  is  with  the  line  running  through 
the  poles,  PP.  But  this  is  not  a  true  circle,  for  the  di- 
ameter EE  is  longer  than  the  diameter  PP.  The  true 
circle  described  by  the  diameter  PP  revolving  on  the 


THE   EAKTH    AS    IT   IS.  81 

centre  c  would  be  PePe.  The  truth  in  regard  to  the 
shape  of  the  earth  is  represented  here,  but  much  exag- 
gerated— how  much  you  shall  see.  The  line  PP  is  on 
the  scale  of  2600  miles  to  the  inch,  to  represent  the  8000 
miles  of  the  earth's  diameter.  Of  course  -^th  of  an  inch 
would  be  260  miles,  and  to  make  the  amount  of  exagger- 
ation alluded  to  above  apparent  to  the  eye,  an  inner  cir- 
cle at  this  distance  from  the  outer  one  is  drawn.  You 
see,  then,  that  a  tenth  of  the  distance  between  the  outer 
and  inner  circle  (3ff)  would  be  26  miles,  and  the  bulging 
of  the  earth  at  the  equator  is  but  half  of  this  amount. 
To  get  at  the  real,  unexaggerated  fact,  then,  you  must 
take  only  the  -^ih  part  of  the  distance  from  e  to  the  in- 
ner circle  to  represent  the  bulging  of  the  earth,  and  this 
would  be  adequately  represented  by  merely  doubling  the 
line  of  the  figure  at  e,  and  letting  it  gradually  diminish  to 
the  single  line  as  you  go  to  the  poles  PP.  But  small, 
comparatively,  as  this  equatorial  bulging  is,  it  is  supposed 
to  be  of  very  great  importance  in  tending  to  keep  the 
earth  always  revolving  uniformly  on  one  axis — the  polar 
axis.  With  the  very  rapid  revolution  of  the  earth  (1000 
miles  every  hour),  and  its  more  rapid  motion  in  its  orbit 
(68,000  miles  every  hour),  even  a  slight  deviation  from 
regularity  in  the  revolution  would  be  attended  with  dis- 
astrous results.  There  are  inferences  to  be  drawn  from 
the  shape  of  the  earth  in  reference  to  its  formation,  but 
these  will  be  spoken  of  in  another  chapter. 

158.  Crust  of  the  Earth. — In  the  crust  of  the  earth,  so 
often  spoken  of  by  geologists,  is  included  all  that  portion 
of  the  globe  of  which  we  have  any  knowledge  through 
their  investigations.  Of  course  we  know  nothing  defi- 
nitely and  certainly  of  the  contents  of  the  interior  of  the 
earth ;  but  great  depths  have  been  reached  in  mining, 
and  besides,  as  you  will  see  in  future  portions  of  this 
book,  there  have  been  upheavals  of  the  crust  which  have 
opened  to  view  vastly  greater  depths  than  the  miner  has 
ever  reached.  The  foundation  of  this  crust  is  every 
D2 


82  GEOLOGY. 

where  rock.  However  deep  may  be  the  cavities  which 
hold  the  water,  there  is  a  rocky  bottom,  and,  dig  wher- 
ever you  will,  rock  is  found  beneath  the  earth  and  sand. 
It  is  said  by  Bakewell  that  "  the  crust  of  the  globe  with 
which  we  are  acquainted  does  not  exceed,  in  comparative 
thickness,  that  of  a  wafer  to  an  artificial  globe  three  feet 
in  diameter." 

159.  Land  and  "Water. — The  surface  of  the  globe  is 
reckoned  as  containing  about  211,000,000  square  miles, 
of  which  about  150,000,000  are  covered  with  water,  and 
61,000,000  appear  as  land.     The  proportion  of  water-sur- 
face to  land-surface  is  nearly  8  to  3. 

160.  Elevations  and  Depressions  in  the  Earth's  Sur- 
face.— The  elevations  in  the  forms  of  hills,  table-lands, 
and   mountains    vary    exceedingly,  the    highest   being 
Mount  Everest,  in  the  Himalaya  range,  which  is  29,000 
feet,  or  five  and  a  half  miles  high.     The  ocean  varies 
much  in  depth,  sometimes  probably  reaching  to  50,000 
feet,  though  no  satisfactory  soundings  have  ever  ascer- 
tained such  a  depth.     The  average  depth  is  somewhere 
from  15,000  to  20,000  feet.     Often  about  the  continents 
there  is  a  fringe,  as  we  may  term  it,  of  shallows.     On  the 
coast  of  the  United  States,  off  the  State  of  New  Jersey, 
there  is  such  a  fringe  80  miles  in  width,  the  depth  at  its 
edge  (where  the  ocean  really  begins)  being  only  600  feet, 
while  the  depth  across  the  ocean,  in  a  line  from  New- 
foundland to  Ireland,  has  been  found  to  be  from  10,000 
to  15,000  feet.    Some  extensive  waters,  also,  between  dif- 
ferent bodies  of  land,  can  not  be  regarded  as  parts  of  the 
ocean.     In  the  waters  separating  Great  Britain  from  Eu- 
rope the  depth  is  less  than  600  feet,  and  in  a  large  part 
of  the  German  Ocean  it  is  only  93  feet.     Similar  facts 
have  been  discovered  in  regard  to  the  waters  between 
Asia  and  the  islands  appended  to  it.     These  should  really 
be  considered  as  a  part  of  the  continent  of  Asia,  and  Great 
Britain  as  a  part  of  the  continent  of  Europe. 

Although  the  projection  of  the  earth  at  the  equator  is 


THE   EARTH    AS    IT   IS.  83 

so  small  compared  with  the  whole  earth,  as  was  shown 
by  Fig.  31,  yet  it  is  much  greater  than  the  mountainous 
projections  on  its  surface,  for  the  amount  of  this  projec- 
tion is  1 3^  miles,  while  the  height  of  the  highest  of  the 
mountains  is  5^  miles.  It  is  to  be  observed,  also,  that  the 
depressions  are  much  greater  than  the  elevations,  with 
the  exception  of  the  grand  equatorial  one,  for  in  some 
cases  they  probably  reach,  as  already  stated,  a  depth  of 
50,000  feet ;  and,  if  the  ocean  were  laid  bare,  we  should 
see  irregularities  like  those  on  the  land,  but  on  a  much 
larger  scale.  Between  the  so-called  Banks  of  Newfound- 
land and  Newfoundland  itself  there  is  one  of  those  deep 
submarine  valleys,  while  at  the  Banks  there  is  a  plateau 
of  rock  that  comes  within  about  250  feet  of  the  surface. 
The  water  on  this  plateau  abounds  in  fish,  which  choose 
such  shallow  places  rather  than  the  deep  ocean  valleys. 
South  of  the  Banks  the  Atlantic  Ocean  reaches  the  im- 
mense depth  of  30,000  feet. 

161.  Arrangement  of  the  Land. — There  are  some  pecul- 
iarities in  the  arrangement  of  the  land  of  the  earth  that 
are  worthy  of  notice.  The  great  bulk  of  it  is  in  the 
northern  hemisphere,  up  about  the  arctic  region,  there 
being  nearly  three  times  as  much  land  north  of  the  equa- 
tor as  there  is  south  of  it.  As  it  extends  from  the  north 
down  into  the  southern  hemisphere  it  narrows  very 
much,  as  seen  in  the  shape  of  North  America  and  Africa, 
which  is  triangular.  The  same  disposition  of  the  land 
is  essentially  carried  out  in  Hindostan  and  other  exten- 
sions southward  of  the  continent  of  Asia.  Notice,  be- 
sides this,  that  the  land  is  really  divided  into  two  great 
parcels,  the  Eastern  and  Western  Continents,  for  Europe, 
Asia,  and  Africa  may  be  regarded  as  one ;  and  that  there 
are  two  great  oceans  between  them,  one  of  them  being 
much  larger  than  the  other.  It  may  be  remarked  here 
that,  in  the  present  state  of  the  world,  it  is  a  very  great 
advantage  and  convenience  to  have  the  narrower  ocean, 
the  Atlantic,  lying  between  those  portions  of  the  world 


84  GEOLOGY. 

which,  from  their  common  civilization,  have  so  much  in- 
tercourse with  each  other.  It  would  be  a  great  bar  to 
this  intercourse  to  have  so  wide  an  ocean  as  the  Pacific 
lying  between  America  and  Europe.  I  have  spoken  of 
the  two  grand  masses  of  land  as  extending  from  the  arc- 
tic region  down  into  the  southern  hemisphere;  but  ob- 
serve that  it  is  not  an  unbroken  extension  of  land.  By 
an  arrangement  of  the  waters,  as  noticed  by  Professor 
Guyot,  there  is  a  band  of  water  from  east  to  west  cut- 
ting the  land  in  two  almost  completely — so  nearly  that 
it  requires  only  two  short  canals  to  be  made  by  man  to 
finish  the  communication.  This  belt  is  composed  of  the 
two  oceans,  the  Mexican  Ocean  in  the  western  hemi- 
sphere, and  the  Mediterranean  Sea,  the  Red  Sea,  and  the 
seas  of  the  East  Indies  in  the  eastern.  You  can  readily 
see  how  this  arrangement  promotes  largely  the  inter- 
course by  water  throughout  the  earth,  and  how  import- 
ant it  is  that  those  parts  of  the  plan  which  the  Creator 
has  purposely  left  to  the  ingenuity  and  enterprise  of  man 
should  be  carried  into  execution. 

162.  Arrangement  of  Mountains — Mountains  are  not 
scattered  about  here  and  there  in  a  confused  manner, 
but  there  is  an  obvious  general  plan  in  their  arrange- 
ment. They  are  to  a  great  extent  placed  in  chains  or 
ranges,  as  you  see  in  the  Rocky  Mountains,  the  Andes, 
the  Appalachians,  the  Pyrenees,  the  Urals,  the  Himala- 
yas, etc.  Perhaps  the  most  remarkable  fact  about  these 
mountain  chains  is  that  they  are  so  arranged  as  to  in- 
close large  basins  of  land  on  the  continents.  Thus  in 
North  America  the  immense  basin  watered  by  the  Mis- 
sissippi and  other  rivers  lies  between  the  great  ranges 
of  mountains  on  the  east  and  the  west.  It  is  this  basin 
arrangement,  with  great  mountain  walls,  that  is  the 
grand  characteristic  of  a  continent  in  distinction  from 
an  island.  Notice  another  great  fact  in  the  arrange- 
ment. The  highest  mountains  are  placed  on  that  side 
of  the  continent  which  is  toward  the  broadest  ocean. 


THE    EARTH    AS    IT   IS.  85 

Thus  the  Rocky  Mountains  are  higher  than  the  range  of 
mountains  which  run  down  from  Maine  to  Georgia, 
called  by  the  general  name  of  the  Appalachian  range. 
So  also,  as  the  Pacific  Ocean  is  broader  opposite  to 
South  America  than  opposite  North  America,  the  Andes 
are  much  higher  than  the  Rocky  Mountains.  The  same 
plan,  essentially,  is  carried  out  in  Africa,  Australia,  and 
also  in  Europe  and  Asia,  though  not  in  so  clear  and  sim- 
ple a  manner. 

There  is  much  variation  in  the  arrangement  of  differ- 
ent ranges  of  mountains.  They  are  more  commonly 
curved  than  straight,  and  the  manner  in  which  the  indi- 
vidual mountains  stand  toward  each  other  is  very  differ- 
ent in  different  cases. 

There  are  certain  prevalent  directions  of  the  chains  of 
mountains,  and  the  same  is  true  of  groups  of  islands, 
which  are  often  really  the  summits  of  submerged  mount- 
ain ranges.  In  the  Pacific  Ocean  they  have  usually  a 
northwesterly  direction,  or  trend,  as  it  is  termed. 

163.  Volcanoes. — Some  mountains  throw  out  occasion- 
ally from  their  summits  large  quantities  of  liquid  lava 
and  matter  in  gaseous  form ;  often  also  solid  rocks,  ash- 
es, mud,  etc.     The  exhibitions  made  in  these  eruptions 
are  among  the  most  magnificent  in  nature.     About  two 
thirds  of  the  volcanoes  are  on  islands,  and  the  greater 
part  of  the  other  third  are  near  the  ocean  on  the  conti- 
nents.    This  nearness  to  water  is  supposed  to  show  that 
steam  must  have  much  to  do  with  the  eruptions,  which 
also  seems  to  be  proved  by  the  fact  that  in  these  erup- 
tions great  quantities  of  steam  escape.     In  Fig.  32  (p.  86), 
in  which  the  shaded  parts  indicate  the  localities  of  vol- 
canoes, not  only  is  their  vicinity  to  the  ocean  shown,  but 
the  fact  that,  like  ordinary  mountains,  they  are  very  often 
arranged  in  ranges. 

164.  Plateaus  and  Lowlands. — Any  extended  region, 
whether  it  be  flat  or  diversified,  if  it  be  much  elevated 
above  the  level  of  the  sea,  is  called  a  plateau,  while  the 


86 


GEOLOGY. 


Fig.  32. 


term  lowland  is  applied  to  regions  that  are  less  than  a 
thousand  feet  above  that  level.  The  great  valley  of  the 
Mississippi,  the  plains  of  the  Amazon,  and  the  pampas 
of  La  Plata,  are  examples  of  the  latter.  Plateaus  some- 
times extend  between  ranges.  Both  plateaus  and  low- 
lands may  have  single  mountains  or  mountain  ridges. 
The  term  table-land  is  often  applied  to  plateaus,  especial- 
ly when  their  surface  is  little  diversified.  One  of  the 
most  elevated  plateaus  in  the  world  is  that  of  Thibet,  ly- 
ing between  the  Himalayas  and  the  Kuen-Luen  Mount- 
ains, the  height  varying  from  11,000  to  15,000  feet.  The 
State  of  New  York  is  a  plateau,  varying  in  height  from 
1500  to  2500  feet.  The  Great  Salt  Lake  lies  in  a  corner 
of  a  plateau  by  the  Rocky  Mountain  range,  which  has  an 
altitude  of  from  4000  to  5000  feet.  There  are  some  lofty 
plateaus  in  South  America.  The  city  of  Quito  is  situa- 
ted on  a  plateau  at  an  elevation  of  nearly  10,000  feet,  and 
the  city  of  Potosi  on  one  at  an  elevation  of  13,330  feet, 
the  Lake  Titicaca  being  on  the  same  plateau  at  the  height 
of  12,830  feet.  We  often  see  the  same  arrangement  in 
a  small  way  among  hills  of  ordinary  size.  An  elevated 
plain  skirts  a  hill,  or  lies  between  hills,  making  a  plateau 
of  small  extent.  There  may  be  a  pond  also  in  such  a 
plain,  like  the  lakes  that  are  sometimes  found  in  the  im- 
mense plateaus. 


THE   EARTH    AS    IT   IS.  87 

165.  Rivers. — Rivers  come  from  mountains  and  pla- 
teaus, and,  having  gathered  the  waters  from  these,  run 
through  the  lowlands  into  the  sea.     There  is  system 
here  as  well  as  in  the  arrangement  of  mountains.     For 
example,  the  great  basin  included  between  the  Rocky 
Mountains  and  the  Apalachian  range  has  a  grand  river 
system,  the  Mississippi  being  its  principal  river.     Then 
there  are  two  other  great  systems  in  North  America,  in 
which  the  St.  Lawrence  and  the  Mackenzie  are  the  chief 
rivers ;  but  these  are  not  as  extensive  as  that  of  the 
grand  basin  of  the  continent.     In  South  America  there 
are  also  three  principal  systems,  that  of  the  La  Plata, 
corresponding  with  that   of  the  Mississippi  in  North 
America,  that  of  the  Amazon  in  the  east,  and  that  of  the 
Orinoco  in  the  north.     The   systematic   arrangement, 
which  is  so  obvious  in  the  case  of  the  large  rivers  of  the 
globe,  exists  as  really  with  the  smaller  rivers,  though, 
from  the  influence  of  local  circumstances,  it  is  not  always 
as  manifest. 

166.  Lakes. — Lakes  are  formed  by  rivers  and  streams 
of  various  sizes,  which  pour  their  waters  into  depressions 
on  the  land  from  which  they  can  not  escape  readily,  in 
some  cases  not  at  all.     These  depressions  are  of  various 
shapes  and  sizes.     Those  from  which  the  water  has  no 
outlet  are  salt  lakes,  as,  for  example,  the  Dead  Sea  in 
Asia,  and  the  Great  Salt  Lake  of  this  country. 

167.  Relation  of  Mountains  to  Fertility. — The  position 
of  mountains  has  a  great  influence  upon  the  fertility  of  a 
country  by  detaining  the  winds  and  condensing  their 
moisture.    Observe  how  the  winds  are  produced.    There 
are  two  principal  causes  of  them,  heat  and  the  rotation 
of  the  earth,  and  consequently  the  winds  that  blow  from 
the  tropics,  or  trades,  as  they  are  called,  are  eastern 
winds,  while  the  winds  coming  from  the  colder  regions 
are  western.     The  winds  from  the  east,  being  warm,  are 
therefore  loaded  with  moisture,  while  the  cold  western 
winds  have  comparatively  little  moisture,  and  continual- 


GEOLOGY. 

ly  gather  or  take  tip  more  as  they  bend  toward  the  equa- 
tor, and  are  therefore  drying  winds.  For  this  reason, 
more  rain  falls  on  the  eastern  side  of  a  continent  than  on 
the  western.  "The  annual  amount  of  rain  in  Europe  is 
32  inches,  while  in  the  temperate  zone  in  the  United 
States,  east  of  the  Mississippi,  it  is  44  inches,  the  differ- 
ence being  still  greater  if  we  compare  the  eastern  part 
of  South  America  with  the  opposite  side  of  the  Atlantic 
Ocean.  You  can  see  now  what  influence  the  mountains 
have  on  fertility  in  the  case  of  the  American  continent. 
Its  highest  mountains  are  on  the  western  side,  and  there- 
fore the  warm  eastern  winds  sweep  with  their  moisture 
over  almost  the  whole  breadth  of  the  continent,  parting 
with  it  here  and  there  from  condensing  influences.  Fer- 
tility is  the  result  of  this  diffusion  over  the  continent  of 
this  moisture,  and  hence  America  is  appropriately  called 
by  Professor  Guyot  the  Forest  Continent.  Where  the 
moisture  deposited  from  the  passing  wind  is  not  enough 
to  produce  forests,  we  have  the  prairies  and  the  pampas. 
Now  if  the  low  Appalachians  were  on  the  west  and  the 
high  Rocky  Mountains  were  on  the  east  of  North  Amer- 
ica, most  of  the  moisture  of  the  trades  would  be  con- 
densed at  once,  and  be  poured  back  into  the  Atlantic 
Ocean,  and  in  that  case  the  great  river  system  of  the 
continent's  basin  would  not  exist,  but  in  place  thereof  a 
desert.  You  can  readily  apply  for  yourself  the  above  ex- 
planation to  the  desert  of  Sahara,  in  Africa,  and  other 
great  deserts,  and  therefore  I  need  not  dwell  farther  on 
this  interesting  subject. 

168.  Circulation  ofWater.— Water  is  every  where  in 
motion  on  the  earth.  Rising  continually  from  every 
point  of  the  surface  by  being  dissolved  in  the  air,  it  is 
brought  down  again  to  the  earth  by  being  condensed 
from  its  vaporous  state.  There  is,  therefore,  a  constant 
circulation  of  the  water  back  and  forth  between  the 
earth  and  its  envelope  of  air.  In  the  earth  itself  it  is 
never  at  rest,  but  insinuates  itself  among  all  loose  parti- 


THE   EARTH    AS    IT   IS.  89 

cles  and  masses,  runs  down  all  declivities  in  streams 
small  and  large  toward  the  ocean,  and  is  agitated  by  the 
winds  and  the  tides.  Not  only  is  its  motion  kept  up  in 
these  ways,  but  there  are  great  systematic  currents  in  the 
ocean,  which  maintain  a  free  circulation  between  differ- 
ent quarters  of  the  globe,  and  exert  a  marked  influence 
upon  the  climates  of  many  countries.  The  great  Gulf 
Stream  is  one  of  these  currents.  By  all  of  these  means 
of  motion  there  is  secured  a  circulation  of  water  in  the 
earth  which  in  its  system  and  thoroughness  bears  an 
analogy  to  the  circulation  of  the  blood  in  the  body. 
What  extensive  and  varied  effects  it  produces  in  this 
circulation  upon  the  solid  materials  of  the  earth's  surface 
you  will  learn  in  succeeding  chapters. 

169.  How  the  Earth's  Surface  is  Diversified. — I  have 
already  spoken  of  some  of  the  grand  features  of  the 
earth's  surface.      But  there   are   subordinate  features 
which  diversify  it  greatly — bluffs,  hills  of  various  con- 
tours, valleys  with  and  without  streams,  collections  of 
rock  differing  in  arrangement,  shape,  and  color,  some  be- 
ing stratified  and  others  not;  rocks  jutting  out  from  the 
ground,  boulders  of  various  sizes,  etc.     A  material  addi- 
tion is  made  to  this  diversity  by  water  every  where  en- 
livening the  scene  by  its  motion  in  obedience  to  every 
impulse.     And  then  we  have  life,  with  its  endless  varie- 
ty of  shape,  and  color,  and  motion. 

170.  Treasures  in  the  Crust  of  the  Earth. — As  you  have 
already  seen,  there  are  precious  treasures  of  every  varie- 
ty scattered  among  the  rocks,  and  earth,  and  sand  of  the 
globe  for  the  use  of  man.     There  are  immense  stores  of 
coal ;  metals  of  every  kind,  and  in  quantities  suited  to  the 
amount  of  uses  to  which  they  can  be  appropriated ;  pre- 
cious gems  of  every  quality  and  hue ;  granite,  sandstone, 
marble,  etc.,  for  building ;  clay  for  pottery  and  bricks, 
etc. 


90  GEOLOGY. 


CHAPTER  X. 

PKESENT   CHANGES   IN   THE   EARTH. 

171.  Ages  of  the  Earth.— The  earth  is  older  than  6000 
years,  as  has  been  absolutely  demonstrated  by  the  re- 
searches of  geologists.     Here  is  an  apparent  discrepancy 
between  what  is  revealed  by  the  works  of  God  and  his 
written  revelation;   but  it   is   only  apparent.     I  shall 
speak  of  this  point  particularly  in  another  place,  and  let 
it  now  suffice  to  say  that  it  is  the  belief  of  most  geolo- 
gists that  the  days  of  Moses  represent  long  ages,  and 
that  the  time  which  has  elapsed  since  the   earth  was 
finally  fitted  for  man  is  a  very  small  period  compared 
with  the  length  of  time  expended  by  the  Creator  in  its 
construction  and  preparation.     It  is  my  intention,  in  this 
chapter,  to  treat  of  those  changes  which  are  matter  of 
observation  and  history.     The  word  present,  in  the  title 
of  the  chapter,  refers  to  the  whole  time  in  which  man 
has  inhabited  the  earth,  in  distinction  from  the  long  pe- 
riods consumed  in  its  preparation  for  his  use.     It  is  not 
always  easy  to  make  this  distinction,  and  some  changes 
will  be  noticed  in  this  chapter  which  began  far  back  of 
the  age  of  man.     This  is  necessary,  because  the  same 
agents  which  prepared  the  world  for  its  present  purpose 
have  produced  all  the  changes  since  man  was  introduced 
upon  the  scene. 

172.  Agents  of  Change. — The  agents  by  which  changes 
are  constantly  produced  in  the  earth  are  heat,  water,  air, 
chemical  processes,  attraction,  electricity,  and  life,  both 
vegetable  and  animal.     The  manner  in  which  they  act 
will  be  developed  as  we  proceed,  and  therefore  I  will 
not  dwell  on  this  subject  here,  but  will  only  notice  in  a 
few  words  the  principal  of  these  agents.    Water  and  air 
are  every  where  kept  in  motion  by  the  influence  of  heat 


PRESENT   CHANGES    IN   THE   EARTH.  91 

and  attraction,  as  was  fully  explained  in  Part  I.  But 
water  has  a  larger  agency  in  producing  the  changes  in 
the  earth  than  air.  Through  the  influence  of  heat  it  is 
carried  up  constantly  into  the  atmosphere  in  evapora- 
tion, and  then  falls  in  rain,  snow,  etc.,  and  in  seeking  its 
level  in  obedience  to  attraction,  effects  a  large  portion  of 
these  changes.  The  influence  of  heat  is  seen  in  the  erup- 
tions of  volcanoes  and  other  phenomena,  and  these  indi- 
cate to  some  extent  the  agency  which  heat  had  in  build- 
ing up  the  earth,  as  do  the  present  effects  of  moving  wa- 
ter what  agency  that  had  in  the  work.  It  is  these  aque- 
ous and  igneous  agencies,  as  they  are  termed,  which,  oft- 
en acting  in  opposition  and  sometimes  in  unison,  have 
for  the  most  part  arranged  and  consolidated  the  mate- 
rials of  the  earth,  so  as  to  put  it  into  its  present  condi- 
tion ;  and  therefore  it  is  necessary  to  view  their  present 
operations,  that  we  may  understand  those  which  were 
carried  on  in  the  ages  that  preceded  the  advent  of  man, 
when  the  earth  was  being  prepared  by  successive  steps 
to  be  his  habitation.  This  will  be,  then,  the  line  of  our 
investigation  in  the  present  chapter. 

173.  Water  Changing  the  Locality  of  Materials. — What 
we  see  in  the  washings  of  every  shower  on  slopes  and 
hill-sides  exemplifies  some  of  the  vast  changes  which  wa- 
ter is  producing  on  a  large  scale  in  the  earth.  Different 
kinds  of  materials  are  moved  according  to  the  different 
degrees  of  rapidity  with  which  the  water  flows.  If  you 
look  at  a  mountain  torrent  you  see  nothing  in  its  course 
but  large  stones,  because  not  only  mud  and  sand,  but 
pebbles  of  considerable  size,  are  carried  along  by  the 
force  of  the  water.  If  you  go  farther  on,  where  the 
stream  is  less  rapid,  you  will  find  the  pebbles,  and  if  the 
rapidity  lessens  as  you  follow  the  stream,  there  will  be 
sand  on  its  bottom ;  and  when  the  water  moves  on  slow- 
ly through  a  plain,  you  will  find  the  sediment  deposited 
to  be  mud.  The  explanation  of  this  sorting  out  of  ma- 
terial by  moving  water  has  been  given  in  §  1 93,  Part  I., 


92  GEOLOGY. 

and  it  is  not  necessary  to  repeat  it  here.  The  pebbles, 
and  sand,  and  mud  moved  by  water  were  all  once  in  solid 
rock,  and  how  the  rocks  are  thus  broken  up  will  be  seen 
hereafter.  The  deposit  of  these  materials  is  regulated 
by  other  varying  circumstances  as  well  as  those  which  I 
have  mentioned,  as  I  will  now  proceed  to  illustrate. 

174.  Deposits  in  Rivers  and  on  their  Borders.  —  A  riv- 
er descending  some  slope  of  considerable  pitch  always 
brings  along  with  it  much  solid  matter,  and  if  it  after- 
ward move  sluggishly  through  a  plain,  this  matter  will 
be  deposited  quite  evenly  over  its  bottom.  If  the  river  be 
narrowed  much  at  any  point  the  water  will  move  so  rap- 
idly there  that  it  will  carry  the  material  suspended  in  it' 
on  beyond,  and  then,  if  it  spread  out  suddenly  over  a 
large  surface,  there  will  be  much  matter  deposited,  ex- 
cept in  the  direct  line  which  the  main  body  of  the  water 
takes.  On  either  side  of  this  channel  —  that  is,  on  the 
flats  —  will  the  most  of  the  deposit  be  made.  In  some 
cases  the  plain  on  either  side  of  a  river  is  so  high  that 
the  water  flows  over  it  only  when  it  is  temporarily  raised 
by  a  freshet.  This  is  termed  the  flood-plain.  In  this 
case  there  is  some  addition  to  the  plain  every  time  that 
a  freshet  occurs,  until  at  length  the  land  is  raised  so  high 
that  the  flood  does  not  overflow  it.  This  process,  year 
after  year,  tends  to  make  that  part  of  the  plain  immedi- 
ately bordering  on  the  river  higher  than  the  rest  of  the 
plain,  because,  the  farther  the  water  is  from  the  river,  the 
less  has  it  suspended  in  it  from  the  settling  of  the  sedi- 
ment which  is  continually  going  on.  And  as  some  of 
the  matter  is  deposited  on  the  bottom  of  the  river  itself, 
the  river  is  gradually  raised,  and  may  be,  after  a  while, 
on  a  level  which  is  above  the  adjoining  land,  except  that 
which  forms  the  banks.  These  results  are  shown  by 

Figs.  33  and  34.    Let 


_  valley,  and  b  a  stream 

Fig.  33.  of  water   which   runs 


PRESENT   CHANGES   IN   THE   EARTH. 


93 


Fig. 


through  it,  occasionally  overflowing  its  banks.     In  the 
overflows  mud  will  be  deposited  over  the  valley-flat,  and 

after  a  while  the  result 
m  indicated  in  Fig.  34 
will  be  realized.  Just 
this  process  has  been 
gone  through  with  along  the  Mississippi,  so  that  there 
is  a  natural  levee,  as  it  is  termed,  on  each  side  of  the 
river.  The  inhabitants  are  obliged  to  raise  this  in  cer- 
tain places  to  prevent  inundations  from  freshets.  Some- 
times a  break  (crevasse)  occurs  in  the  levee,  and  much 
damage  is  done  in  the  country  adjoining.  The  same 
process  goes  on,  and  the  same  results  occur  at  length  in 
those  cases  where  the  land  along  a  river  is  inundated  at 
all  seasons. 

175.  Improvement  of  Rivers. — A  very  pretty  illustra- 
tion of  the  manner  in  which  the  solid  material  in  rivers 
is  deposited  is  furnished  us  by  a  mode  of  improving  river 
navigation  sometimes  practiced.  We  will  take  a  particu- 
lar case.  The  river  issues  from  a  gorge,  and  then  spreads 
out  over  a  large  flat  surface,  there  being,  of  course,  a  chan- 
nel through  the  flat  for  the  main  body  of  the  water  to 
flow  in.  The  object  of  the  plan  of  improvement  is  to 
prevent  accumulation  of  sediment  in  the  channel,  and. 
even,  if  possible,  to  carry  out  sediment  already  deposit- 
ed. This  is  done  by  building  piers  of  stone  across  the 
flats  out  toward  the  channel,  as  indicated  in  Fig.  35. 


Fig.  35. 


Let  a  be  the  gorge,  c  c  the  flats  across  which  the  piers 
stretch,  as  represented,  and  b  the  channel.  The  piers,  d, 
d,  d,  it  is  obvious,  will  somewhat  detain  the  water  on  the 
flats,  and  so  allow  the  sediment  to  fall  from  it  in  larger 


94  GEOLOGY. 

amount  than  it  otherwise  would ;  and  this  detention  at 
the  sides  of  the  channel  will  cause  more  water  to  flow 
through  it,  and  to  flow  more  rapidly.  Then,  as  the  flats 
fill  up  with  sediment,  this  effect  upon  the  flow  in  the 
channel  will  continually  increase. 

176.  Deposits  in  Lakes. — In  every  lake  there  is  more 
or  less  deposit  of  sediment  from  the  river  or  rivers  that 
flow  into  it,  and  also  from  all  smaller  streams  that  do  so, 
even  to  the  little  rill  temporarily  made  by  a  shower. 
The  tendency,  then,  is  to  fill  up  the  lake,  and  in  time  the 
result  would  be  the  conversion  of  the  lake  into  a  river. 
If  a  lake  have  a  river  entering  at  one  end  and  issuing 
at  the  other,  the  deposit  is  made  in  that  part  of  it  where 
the  river  enters,  and  the  extent  to  which  it  reaches  de- 
pends on  circumstances.  The  more  rapid  the  entering 
river,  and  the  more  shallow  the  lake,  the  greater- will  be 
the  space  over  which  the  deposit  will  be  made.  The  wa- 
ter of  the  entering  river  is  of  course  turbid,  while  that 
of  the  issuing  river  is  clear,  the  sediment  being  all  depos- 
ited long  before  the  water  reaches  that  end  of  the  lake. 
In  the  Lake  of  Geneva,  which  is  thirty-seven  miles  long, 
and  varies  in  breadth  from  two  to  eight  miles,  we  have 
all  this  exemplified.  The  Rhone  enters  it  muddy,  but  it 
issues  beautifully  clear  at  the  city  of  Geneva.  The  ra- 
pidity with  which  the  filling  up  goes  on  may  be  judged 
of  by  the  fact  that  the  town  of  Port  Vellais,  which,  eight 
centuries  ago,  was  on  the  edge  of  the  lake,  is  now  more 
than  a  mile  and  a  half  distant  from  it.  The  great  lakes 
of  this  country  are  continually  growing  smaller.  There 
are  facts  which  show  that  their  shores,  in  many  places, 
were  once  far  away  outside  of  where  they  now  are. 
There  is,  for  example,  south  of  Lake  Erie,  and  distant 
from  it  from  four  to  eight  miles  at  different  points,  a 
ridge  made  up  of  sand,  gravel,  and  rounded  pebbles,  just 
as  the  shore  of  the  lake  is  now.  Moreover,  when  wells 
are  dug,  or  any  excavations  made  in  this  ridge,  there  are 
found  deeply  buried  in  the  soil  pieces  of  decayed  wood, 


PRESENT    CHANGES    IN    THE    EARTH. 


95 


small  and  large,  and  such  shells  as  are  now  met  with  in 
the  lake. 

177.  Deltas. — The  name  delta  is  commonly  given  to 
the  accumulation  from  a  river  at  its  mouth  as  it  empties 
into  a  sea  or  the  ocean,  when  it  has  gone  so  far  as  to  form 
flats,  through  which  the  river  runs  usually  with  a  net- 
work of  channels.  The  name  is  given  from  the  common 
resemblance  in  the  form  of  this  accumulation  to  the  Greek 
letter  A,  which  is  called  Delta.  The  shape  which  the  de- 
posit tends  to  take  is  fairly  represented  by  Fig.  36.  From 


Fig.  36. 


the  point  where  the  river  enters  the  sea  the  sedimentary 
matter  spreads  out  or  radiates,  and  at  the  same  time  it  is 
tossed  about  and  beaten  back  by  tides  and  the  waves.  It 
is  this  action  of  the  sea,  in  opposition  to  the  prolongation 
of  the  river  current  into  it,  that  produces  the  bars  so  often 
found  in  such  cases.  These  bars  are  indicated  in  the  fig- 
ure at  the  sea-extremity  of  the  delta.  The  numerous  sand- 
bars formed  at  the  mouth  of  the  Mississippi  render  the  en- 
trance to  it  difficult  and  hazardous.  Sometimes  even  isl- 
ands are  formed.  Thus,  about  fifty  years  ago,  an  island 
was  formed  opposite  the  mouth  of  the  Hoogly  River, 
which  in  1818  was  two  miles  long  and  half  a  mile  wide, 
was  covered  with  vegetation,  and  was  inhabited ;  but 
afterward  this  was  gradually  swept  away,  and  dwindled 
to  a  mere  small  sand-bank.  It  is  common  there,  and  in 
other  cases  also,  for  islands  to  form,  and  then  be  de- 
stroyed by  the  change  of  currents  from  the  formation 


96  GEOLOGY. 

of  new  islands.  There  is  no  delta  formed  at  the  mouth 
of  the  Amazon,  because  there  is  an  ocean  current  that 
sweeps  by,  and  this  carries  the  sediment  discharged  by 
that  river  up  by  the  coast  of  Guiana,  where  it  is  deposit- 
ed, forming  immense  muddy  shoals  and  swampy  tracts. 

178.  Amounts  of  Deposits  from  Rivers. — The  amount 
of  sediment  deposited  by  large  rivers  is  enormous.    The 
Ganges  pours  such  a  quantity  of  mud  and  sand  into  the 
Bay  of  Bengal  that  the  water  is  seen  to  be  colored  by 
it  sixty  miles  from  the  shore.     It  is  calculated  that  in 
the  rainy  season  each  year  this  river  discharges  into  the 
sea  an  amount  of  solid  matter  equal  in  weight  to  fifty-six 
pyramids,  estimating  a  pyramid  to  contain  6,000,000  of 
tons  of  granite.     Mr.  Lyell  states  that  "  if  a  fleet  of  more 
than  eighty  Indiamen,  each  freighted  with  one  thousand 
four  hundred  tons  weight  of  mud,  were  to  sail  down  the 
river  every  hour  of  every  day  and  night  for  four  months 
continually,  they  would  only  transmit  from  the  higher 
country  to  the  sea  a  mass  of  solid  matter  equal  to  that 
borne  down  by  the  Ganges  in  the  flood  season,  as  the 
exertions  of  a  fleet  of  about  two  thousand  such  vessels 
going  down  daily  with  the  same  burden,  and  discharg- 
ing it  into  the  gulf,  would  be  no  more  than  equivalent  to 
the  operations  of  the  great  river.     Yet,  in  addition  to 
this,  it  is  probable  that  the  Burrampooter  conveys  an- 
nually as  much  solid  matter  to  the  sea  as  the  Ganges." 
The  amount  of  land  made  by  such  enormous  quantities 
of  sediment  is  very  great.     Most  of  the  lower  part  of 
Louisiana  was  formed  by  sediment  brought  down  by  the 
Mississippi,  and  the  land  has  encroached  upon  the  water 
several  leagues  since  New  Orleans  was  built.     The  solid 
matter  annually  discharged  by  the  Mississippi  is  two 
thousand  million  (2,000,000,000)  tons.     This  is  sufficient 
to  cover  a  township  six  miles  square  with  earth  thirty 
feet  deep. 

179.  Extent  of  Deltas.— The  deltas  of  very  large  riv- 
ers are  of  great  extent.     That  of  the  Nile  is  about  as 


PRESENT    CHANGES    IN    THE    EARTH.  97 

large  as  the  State  of  Vermont.  That  of  the  Ganges  is 
much  larger,  being  220  miles  long,  and  having  a  base  on 
the  sea  of  200  miles.  It  is  bounded  on  either  side  by  an 
arm  of  the  Ganges,  and  near  the  sea  it  is  intersected  by 
a  net-work  of  rivers  and  creeks,  and  is  a  resort  for  croc- 
odiles and  tigers.  The  material  constantly  brought  down 
the  river  is  encroaching  upon  the  sea,  and  it  now  forms 
a  slope  extending  out  about  a  hundred  miles.  This  real- 
ly ought  to  be  taken  into  the  account  in  estimating  the 
extent  of  the  formation. 

180.  Consolidation  of  Deposits.  —  In  some  cases  the 
consolidation  into  rock  of  the  deposits  of  sediment  by 
water  is  going  on  at  the  present  time,  especially  where 
there  is  mingled  with  the  sand  and  mud  some  agglutina- 
ting material  like  carbonate  of  lime.     From  this  cause 
there  is  rock  continually  forming  in  the  sediment  dis- 
charged by  the  River  Rhone.     In  the  Museum  at  Mont- 
pellier  there  is  a  cannon  which  was  taken  from  the  sea 
near  the  Rhone's  mouth  incased  in  a  crystalline  calcare- . 
ous   matter,  and  having   scattered  through   it   broken 
shells.     But  the  whole  subject  of  the  consolidation  of 
mud  and  sand  into  rock  will  be  treated  of  hereafter,  and 
I  will  not  dwell  upon  it  farther  here. 

181.  Water  Encroaching  upon  Land. — Thus  far  I  have 
spoken  only  of  the  encroachment  of  land  upon  water  by 
the  deposit  of  material  brought  to  lakes  and  the  sea  by 
rivers.     But  there  is  sometimes  the  opposite  effect — the 
wearing  away  of  land  by  the  action  of  water.     Much  of 
the  eastern  coast  of  England  is  wearing  away,  and  many 
localities   of  towns   have   disappeared   in   the  German 
Ocean.     Some  of  the  coast  of  Long  Island  is  encroached 
upon  rapidly  by  the  sea ;  and  at  Cape  May,  in  Delaware, 
land  is  destroyed  at  the  average  annual  rate  of  nine  feet. 
Sullivan's  Island,  South  Carolina,  was  worn  away  in  three 
years  to  the  extent  of  a  quarter  of  a  mile.     Some  of  the 
Shetland  Isles  have  been  destroyed  by  the  sea,  and  the 
granite  rocks  of  some  of  them  that  are  now  wasting 

E 


98 


GEOLOGY. 


away,  standing  up  in  the  midst  of  the  water,  look  in  the 
distance  like  fleets  of  vessels.  On  the  coast  of  France, 
especially  in  Brittany,  where  the  tides  rise  to  a  great 
height,  the  sea  is  constantly  encroaching  upon  the  land, 
and  occasionally  does  so  to  a  large  extent.  In  the  ninth 
century  many  villages  were  carried  away.  Great  changes 
have  occurred  in  Holland  from  time  to  time,  the  land 
sometimes  gaining  upon  the  sea,  and  sometimes  the  re- 
verse. At  one  time  the  tide,  breaking  through  a  dam, 
overflowed  seventy-two  villages,  and  irretrievably  de- 
stroyed thirty-five  of  them.  Other  examples  in  abund- 
ance might  be  cited,  but  these  will  suffice. 

182.  Erosive  Power  of  Water. — Water,  acting  by  it- 
self mechanically,  exhibits  in  the  course  of  time  great 
erosive  results.  The  hardest  rocks  can  not  resist  it,  much 
less  the  softer  ones.  The  Pulpit  Rock,  so  called,  at  N"a- 
hant,  Mass.,  seen  in  Fig.  37,  is  an  example  of  the  erosive 


Fig.  37. 

action  of  the  waves  continually  dashing  against  it  year 
after  year.     But  little  of  the  rock  is  worn  away  each 


PJBESENT   CHANGES    IN   THE   EARTH.  99 

day,  but  this  little  daily  work  sums  up  largely  when  con- 
tinued through  centuries.  Water  does  much  erosive 
work  by  rubbing  one  solid  surface  against  another.  This 
we  see  on  the  sea-shore,  as  the  waves,  lashing  the  shore, 
jostle  the  pebbles,  great  and  small,  against  each  other. 
The  same  thing  is  done  with  the  grains  of  sand  and  mud 
wherever  there  is  water  moving  them.  Every  pebble 
and  grain  that  is  carried  down  by  a  river  toward  the 
sea  grows  continually  smaller  by  being  rubbed  on  its 
passage  by  the  accompanying  grains  and  pebbles,  as  well 
as  by  the  friction  of  the  water  itself.  We  see  this  mode 
of  erosion  exemplified  in  the  pot-holes  seen  in  rocks 
where  there  is  shallow  water  running  over  them.  The 
stones  contained  in  them  are  rounded  by  the  constant 
friction,  and  at  the  same  time  wear  the  hole  in  the  rock 
continually  larger.  In  the  Franconia  Notch  of  the  White 
Mountains  there  is  a  pot-hole  in  granite,  called  the  "  Ba- 
sin," which  is  fifteen  feet  deep  and  about  twenty  in  di- 
ameter. 

183.  Niagara  Falls. — One  of  the  most  striking  exam- 
ples of  the  erosive  power  of  water  we  have  in  the  Falls 
of  Niagara.  The  river  runs  over  hard  limestone,  but 
under  this  are  soft  shales.  The  result  is  that  the  water 
at  the  Falls  continually  wears  away  the  shales,  and  the 
limestone  falls  from  want  of  support  below,  the  water 
above  pressing  it  downward.  The  edge  of  the  fall  is 
therefore  constantly  receding  at  a  rate  calculated  vari- 
ously by  different  persons,  from  one  foot  to  three  feet 
annually.  This  is  a  slow  recession,  but  in  the  course  of 
centuries  the  change  is  a  great  one.  There  is  the  most 
decided  proof  that  the  Falls  were  once  seven  miles  far- 
ther down  the  river  than  they  are  now,  so  that  they 
have  receded  all  that  distance,  the  process  having  begun 
long  ages  before  the  creation  of  man.  As  the  layers  of 
rock,  instead  of  being  perfectly  horizontal,  dip  a  little  in 
running  back  toward  Lake  Erie,  the  height  of  the  fall  is 
constantly  lessening  as  it  recedes.  It  can  therefore  nev- 


100  GEOLOGY. 

er  recede  entirely  to  the  lake,  because,  before  it  reaches 
there,  the  fall  will  cease  to  be  sufficient  for  the  wearing 
away  of  the  shales  underlying  the  limestone. 

184.  Canons  of  Colorado. — The  case  just  cited  of  ero- 
sion by  water,  though  so  striking,  is  by  no  means  so 
strong  a  one  as  some  others ;  for,  while  the  rocks  eroded 
by  the  water  of  the  fall  are  soft,  there  are  instances  of 
vast  and  rapid  erosion  in  solid  tough  rock.     The  stron- 
gest example  is  in  the  canons  of  Colorado,  which  are  riv- 
ers running  between  perpendicular  walls  of  rock,  as  rep- 
resented in  Fig.  38,  in  some  cases  standing  even  6000 
feet  in  height.     These  passages  through  the  rocks  were 
actually  worn  by  the  water,  incredible  as  it  may  at  first 
thought  appear.     We  have  some  comparatively  recent 
erosions,  which  show  that  such  monstrous  erosions  are 
possible,  if  there  be  a  sufficient  length  of  time  allowed 
for  them.     For  example,  the  River  Simeto,  having  been 
dammed  up  by  an  eruption  from  Mount  Etna  in  1603, 
cut  a  passage  through  hard  blue  basaltic  rock  in  a  little 
over  two  centuries,  which  w7as  from  fifty  to  several  hun- 
dred feet  in  width,  and  in  some  places  fifty  feet  deep. 
It  is  rather  difficult  to  realize  that  water  can  accomplish 
such  an  amount  of  erosion,  but  a  little  reflection  on  some 
common  results  with  which  we  are  familiar  will  help  us 
to  do  this.     We  see  the  stone  steps  of  public  buildings 
very  soon  worn  by  the  friction  of  the  many  feet  that  pass 
over  them.     But  this  friction  is  not  constant ;  it  is  so  in- 
termittent that  it  occupies  but  a  small  portion  of  the  time 
that  passes  from  day  to  day.     If  it  were  constant,  the 
stone  would  soon  be  so  much  worn  as  to  require  being 
replaced  by  another.     Now  the  friction  of  water  erodes 
stone  like  the  friction  of  footfalls;  and  if  it  be  constant 
through  century  after  century — perhaps  age  after  age — 
the  erosion,  we  can  see,  will  be  great  in  amount. 

185.  Rocks  Disintegrated  by  Frost. — As  there  are  crev- 
ices and  interstices  in  rocks,  the  water  enters  into  these, 
and  in  cold  weather  becomes  frozen  there.     In  freezing, 


PRESENT    CHANGES    IN    THE    EARTH. 


101 


Fig.  38. 


as  you  learned  in  §  329,  Part  I.,  it  increases  in  bulk.  The 
result  of  this  expansion  of  the  water  is  that  it  tears  the 
rocks  in  pieces,  the  fragments  being  of  all  sizes,  from 


10'2  GEOLOGY. 

grains  up  to  even  large  masses.  The  softer  rocks,  as  the 
shales,  are  broken  into  small  fragments  as  the  water  gets 
into  their  numerous  small  interstices ;  but  in  the  case  of 
the  harder  rocks,  the  water  enters  cracks  and  crevices 
that  it  finds  here  and  there,  and  the  fragments  separated 
by  the  frost  are  of  considerable  size.  It  is  chiefly  from 
this  action  of  frost  on  rocks  that,  at  the  foot  of  such  rocky 
fronts  as  are  presented  by  East  and  West  Rock  at  New 
Haven,  and  by  the  Palisades  of  the  Hudson  River,  there 
are  accumulations  of  fragments  of  rock  of  various  sizes. 
Such  an  accumulation  is  called  a  talus.  In  Fig.  39  one 

of  these  is  represented. 
You  see  a  difference  in 
size  of  the  stones  in  dif- 
ferent parts  of  this  talus. 

^sa==^_B€r^  ^  This  results  from  the  fact 

Fig.  39.  that  every  agitation  from 

the  falling  of  the  fragments,  and  the  action  of  water  and 
wind,  tends,  by  friction,  to  make  the  fragments  smaller, 
and  to  remove  the  smallest  of  them  away  from  the  foot 
of  the  rock.  Some  of  them  are,  in  process  of  time,  con- 
verted into  sand,  and  even  fine  powder,  and  these  the 
rains  may  remove,  or  the  tides,  if  the  foot  of  the  rock  be 
so  situated  as  to  be  exposed  to  them. 

186.  Chemical  Action  of  Water.  —  Water  ordinarily 
contains  dissolved  in  it  both  solids  and  gases,  which  en- 
able it  to  act  chemically  upon  the  rocks.  For  example, 
the  limestone  or  calcareous  rocks  are  acted  upon  by  wa- 
ter containing  carbonic  acid  gas  in  it ;  and  as  rain,  falling 
through  the  air,  becomes  charged  with  this  gas,  which  it 
finds  there,  water  is  continually  carrying  off  calcareous 
matter  from  such  rocks,  supplying  thus  the  sea  with  ma- 
terial for  the  shells  of  the  animals  that  live  in  it  in  such 
abundance  with  these  coverings  upon  them.  Water  thus 
charged  also  acts  with  facility  upon  the  oxyds  and  sul- 
phurets  of  iron  which  are  so  often  present  in  rocks,  and 
also  upon  the  alkalies  that  enter  into  the  composition  of 


n 

PEESENT    CHANGES    IN   THE    EARTH^  .      103 

the  feldspathic  rocks,  so  that  even  the  harder  i\pcks  are 
not  full  proof  against  the  chemical  action  of  waiter.  It 
is  from  this  action  on  these  rocks  that  the  silex  is  pro- 
vided for  the  grains,  and  grasses,  and  other  plants,  in  a 
condition  to  be  dissolved  and  carried  up  the  plant  in  the 
sap.  Even  the  granite,  of  which  man  constructs  his  most 
enduring  monuments,  is  every  where  being  slowly  worn 
away  by  this  action,  and  thus  ever  furnishes  its  quota  of 
fertility  to  the  soil  in  the  alkali  and  clay  that  come  from 
its  decomposing  feldspar. 

187.  Weathering. — This  is  a  term  which  includes,  to 
some  extent,  the  mechanical  action  of  water  with  its 
chemical.  The  idea  is  that  rocks,  on  exposure  to  the 
weather — that  is,  to  rain  and  air,  are  more  or  less  disin- 
tegrated, and  sometimes  even  changed  in  chemical  con- 
stitution, either  at  the  same  time  or  after  the  disintegra- 
tion. This  weathering  is  sometimes  exhibited  in  a  very 
striking  manner  by  ancient  monuments.  This  is  the  case 
with  the  Druidical  monuments  in  the  north  of  England, 
which  are  constructed  of  a  very  hard  rock  called  mill- 
stone grit.  Three  monstrous  pillars,  called  the  Devil's 
Arrows,  having  had  the  rain  beating  upon  them  for  two 
thousand  years,  are  furrowed  deeply  all  down  their  sides, 
the  furrows  being  deepest  at  their  summits,  and  becom- 
ing wider  and  less  distinct  toward  the  bottom.  Crags 
of  rock  too  hard  to  crumble  under  the  weathering  often 
present  the  same  furrows.  Where  rocks  are  porous,  and, 
as  we  may  say,  loosely  constructed,  as  are  many  sand- 
stones, the  disintegration  of  weathering  goes  on  largely 
and  rapidly,  and  we  have  in  such  localities  impercepti- 
ble gradations  from  earth  to  solid  rock.  This  may  be 
seen  often  where  the  rocks  jut  out  from  the  soil,  but 
more  especially  in  digging  down  through  the  success- 
ive gradations  of  soil  and  crumbling  rock  to  the  hard 
rock  itself.  The  same  weathering  which  disintegrates 
the  rocks  does  the  same  work  among  the  fragments  of 
rock,  small  and  great,  in  the  soil,  for  both  water  and  air 


104  GEOLOGY. 

are  present  there.  Sometimes  stones  scale  off  from  this 
weathering  process.  In  many  cases  this  occurs  in  a  very 
regular  manner.  A  beautiful  example  of  this  I  found  in 
a  boulder  of  greenstone  nearly  two  feet  in  diameter.  It 
had  a  covering,  in  the  form  of  a  shell,  of  about  a  third  of 
an  inch  in  thickness,  of  the  same  composition  with  the 
boulder  itself.  Parts  of  this  shell  had  been  broken  off. 
but  it  was  evident  that  it  had  been  whole  quite  recently, 
The  first  thought  of  any  one  that  had  no  knowledge  of 
such  results  of  weathering  would  be,  that  the  boulder 
had  in  some  way  received  a  coating  of  stone ;  but  this 
could  not  in  any  way  occur,  and  we  are  shut  up  to  the 
conclusion  that  this  rind,  as  we  may  call  it,  of  the  boul- 
der was  separated  from  the  body  of  the  stone  by  the 
weathering  process. 

It  is  supposed  that  the  famous  Loggan,  or  rocking 
stones,  referred  to  in  §  100,  Part  I.,  have  been  shaped  so 
as  to  rock  by  this  weathering.  If  a  rock  having  a  small 
base  rest  upon  another,  the  weathering  will  be  apt  to  go 
on  quite  rapidly  on  the  under  side,  from  the  dampness 
and  the  continued  shade,  and  the  base  may  after  a  while 
become  so  narrow  that  the  rock,  though  a  large  one,  may 
be  easily  moved  back  and  forth  upon  it. 

188.  Glaciers. — Having  spoken  of  the  effects  of  water 
in  its  liquid  state,  I  pass  now  to  consider  those  which 
are  produced  by  it  in  its  solid  condition.  You  will  find 
in  another  chapter  that,  great  as  these  effects  are  at  the 
present  time,  they  were  vastly  greater  in  ages  of  the 
world  long  gone  by.  Both  glaciers  and  icebergs  had  a 
large  agency  in  preparing  some  portions  of  the  earth  for 
the  use  of  man. 

A  glacier  is  simply  a  river  of  ice.  It  flows  down  a 
valley  from  the  regions  of  eternal  snow  and  frost  above. 
It  does  not  merely  slide,  for  the  ice  is  somewhat  plastic, 
and  so  bends  to  accommodate  itself  to  the  different 
widths  of  the  valley  and  to  uneven  surfaces.  The  flow, 
it  is  true,  is  very  slow,  but  it  is  constant ;  else  the  snow 


PRESENT   CHANGES    IN   THE   EARTH.  105 

that  feeds  it  above  would  increase  from  year  to  year. 
The  rate  of  flow  varies  from  varying  circumstances. 
Professor  Hughes  built  a  house  on  a  glacier,  and  he 
found  it  to  move  during  fifteen  years  at  the  average  rate 
of  eight  inches  daily,  or  over  three  quarters  of  a  mile 
during  the  whole  time.  A  glacier  is  made  out  of  snow 
which  becomes  consolidated  into  ice,  partly  by  pressure 
and  partly  by  the  infiltration  of  water,  which,  by  freez- 
ing, unites  all  the  grains  of  snow  together.  In  Fig.  40 
(p.  106)  is  represented  one  of  the  grand  glaciers  of  the 
Swiss  Alps,  the  glacier  of  the  Viesch.  A  glacier  carries 
along  whatever  of  loose  material  it  finds  in  its  course, 
and  therefore  there  is  always  a  row  of  loose  stones,  of 
various  size,  lying  along  upon  the  ice  on  each  side  of  the 
glacier.  These  are  called  the  lateral  moraines.  In  the 
glacier  of  the  Yiesch  there  is,  as  you  see,  a  row  of  stones 
along  the  middle.  This,  which  is  called  a  medial  mo- 
raine, arises  from  the  union  of  two  glaciers  in  one,  as 
two  rivers  of  water  unite.  In  this  case  the  two  lateral 
moraines  of  the  glaciers  which  are  adjacent  to  each  other 
unite  at  the  confluence. 

189.  Termination  of  a  Glacier. — The  colder  is  the  cli- 
mate the  farther  down  does  the  glacier  extend.  The 
termination  is  higher  up  in  the  summer  than  in  the  win- 
ter, and  it  varies  in  different  seasons,  according  to  the 
temperature  of  the  season.  The  locality  of  the  end  varies 
sometimes  even  miles  in  the  course  of  a  series  of  years. 
The  glacier  is  sometimes  spoken  of  as  retreating,  but  this 
language  is,  of  course,  not  strictly  correct,  for  there  can 
be  no  movement  backward.  The  apparent  retreat  is 
owing  to  the  melting  of  the  lower  part  of  the  glacier  to 
a  higher  point  than  before.  Toward  the  termination  of 
a  glacier  the  moraines  become  less  and  less  distinct  from 
the  melting  of  the  ice,  and  at  the  very  end  there  issues  a 
stream  of  water,  carrying  along  with  it,  to  a  greater  or 
less  distance,  much  of  the  loose  material  which  the  gla- 
cier has  brought  down  from  the  rocks.  The  stream 
E  2 


106 


GEOLOGY 


Fig.  40. 


PRESENT   CHANGES    IN   THE 


which  comes  from  the  glacier  of  the  Viesch  is  seen  in 
Fig.  41. 


Fig.  41. 

190.  Effects  of  Glaciers. — Fragments  of  rock  of  vari- 
ous sizes,  from  large  stones  to  pebbles,  and  even  sand, 
become  imbedded  in  the  bottom  and  on  the  sides  of  the 
glacier.  These,  held  firmly  in  the  ice,  rub  on  the  bottom 
and  sides  of  the  valley,  and  when  these  are  laid  bare  by 
the  melting  of  the  glacier  toward  its  termination,  the 
rocks  exhibit  varous  marks,  as  grooves,  stria3,  scratches, 
roundings,  smoothings,  etc.,  according  to  the  shape  and 
character  of  the  fragments  that  have  been  brought  in 
contact  with  them  under  the  immense  pressure  of  the 
glacier.  Stones  that  are  loose  are  crushed  and  ground 
to  sand,  some  even  to  mud.  Fig.  42  (p.  108)  shows  the 
side  of  a  glacier  valley  after  the  melting  of  the  glacier. 
The  rocks  are  striated,  smoothed,  and  rounded  wherever 
the  ice  has  been,  while  the  portions  which  were  above 
its  reach  present  the  usual  rough  and  ragged  appearance 
of  hard  rocks. 

All   the    crushed    and   ground   matter    is    at   length 


108 


GEOLOGY. 


Fig.  42. 

brought  to  the  termination  of  the  glacier,  together  with 
the  stones  imbedded  in  the  ice  and  those  accumulated 
on  the  surface.  Much  of  the  finer  matter  is  carried 
away  by  the  stream  of  the  glacier,  to  be  deposited  here 
and  there,  while  the  more  bulky  parts  are  heaped  up  at 
the  end  of  the  glacier  in  what  is  called  the  terminal  mo- 
raine. As  the  limit  of  the  glacier  varies,  as  already 
stated,  very  much  from  year  to  year,  these  terminal  de- 
posits are  scattered  in  heaps  over  quite  a  large  space, 
and  are  much  changed  from  time  to  time  by  the  moving 
ice  and  water. 

191.  Icebergs. — In  very  cold  regions  the  glaciers  ex- 
tend down  to  the  very  borders  of  the  sea,  and  the  end 
of  a  glacier  breaking  off  into  the  water,  forms  an  ice- 
berg. Icebergs  are  of  various  sizes,  many  of  them  reach- 
ing a  height  of  200,  some  even  300  feet  above  the  sur- 
face of  the  water.  As,  from  the  specific  gravity  of  ice, 
only  one  twelfth  of  it  is  above  the  surface,  we  see  only  a 
small  part  of  an  iceberg.  For  the  300  feet  that  we  see 
there  are  3300  feet  (considerably  over  half  a  mile)  be- 
neath the  surface  of  the  water.  A  representation  of  an 
iceberg  seen  by  CaDtain  Ross  is  given  in  Fig.  43.  Ice- 


PRESENT   CHANGES   IN    THE    EARTH.  109 


Fig.  43. 


bergs  are  sometimes  very  extensive.  A  French  expe- 
dition measured  several  which  were  a  mile  in  breadth, 
and  one  which  was  13  miles  long  and  100  feet  high. 
Icebergs  appear  often  in  great  numbers.  Scoresby 
counted  500  of  them  starting  from  the  frozen  regions  at 
one  time  for  the  south.  Dr.  Kane  saw  280  in  Baffin's 
Bay  at  one  time.  Like  glaciers,  icebergs  are  more  or 
less  loaded  with  fragments  of  rock,  great  and  small,  and 
this  load  is  dropped  in  the  sea  as  the  iceberg  melts.  It 
is  supposed  that  the  Banks  of  Newfoundland  were  in 
great  part  made  by  deposition  from  icebergs,  and  the 
accumulation  is  constantly  going  on.  These  bergs  not 
only  drop  material,  but  they  grind  much  of  it  up  into 
sand,  and  even  mud,  by  dragging,  as  they  often  do,  on 
the  floor  of  the  sea.  Sometimes  they  are  stranded,  and 
then,  moved  by  the  waves,  they  roll  back  and  forth,  stir- 
ring up  the  muddy  bottom,  and  crushing  any  fragment 


110  GEOLOGY. 

of  rock  that  icebergs  may  have  dropped  there.  Captain 
Couthoy  saw  one  stranded  on  the  Grand  Bank,  and  the 
water  was  charged  with  mud  at  the  distance  of  a  quar- 
ter of  a  mile. 

192.  Water  a  great  Leveler.  —  By   the  various  ways 
which  I  have  mentioned,  water  is  continually  making 
additions  to  the  comminuted  solids  of  the  earth,  the 
sands,  and  the  soils.     This  is  going  on  in  a  large  way  by 
the  deposit  of  sediment  by  large  rivers,  by  the  streams 
at  the  terminations  of  glaciers,  and  by  the  grindings  of 
icebergs.     But  much  more  of  this  is  effected  in  the  ag- 
gregate by  what  water  is  doing  in  a  small  way  in  every 
part  of  the  earth's  surface.    The  weathering  that  is  done 
all  around  you  every  day  is  the  representative  of  vast 
operations  that  are  gradually  changing  matter  in  form, 
locality,  and  properties  over  the  whole  globe.    The  tend- 
ency of  all  this,  on  the  whole,  is  to  bring  the  heights  of 
the  earth  down,  so  that  water  may  be  called  the  great 
leveler.     If  there  were  no  operations  going  on,  or  to  be 
instituted,  in  opposition  to  this  tendency,  in  time  the  sol- 
id matter  of  the  earth  would  be  one  level,  the  oceans 
being  filled  up  with  the  ruins  of  the  rocks,  the  water 
therefore  covering  up  the  land,  and  making  a  universal 
ocean.     It  would  require  long  ages,  it  is  true,  to  produce 
this  result,  but  it  would  finally  come.     What  operations 
tend  to  prevent  this  will  be  seen  farther  on. 

193.  Agency  of  Heat.  —  As  water  generally  exerts  a 
leveling  influence,  heat  elevates,  and  thus  tends  to  pre- 
serve the  equilibrium  in  the  earth's  crust.     While  water 
wears  down  rocks,  volcanoes  are  throwing  up  melted 
rock  to  be  consolidated  as  it  cools ;  and  earthquakes, 
which  are  connected  with  volcanic  action,  lift  up,  as  you 
will  soon  see,  vast  tracts  of  country  to  a  higher  level, 
while  the  same  elevating  process  is  going  on  in  other 
tracts  in  a  gradual  manner.    The  opposition  of  the  aque- 
ous and  igneous  agencies  will  be  more  obvious  when  we 
come  to  consider  their  operation  in  the  construction  of 
the  earth  in  the  ages  long  gone  by. 


PKESENT   CHANGES    IN   THE   EARTH.  Ill 

194.  Volcanoes. — The  most  striking  present  manifest- 
ations  of  the   agency  of  heat  we  have  in  volcanoes. 
These  are  the  grand  chimneys  of  the  earth;  and,  as  vents 
for  the  great  furnace  of  fire  in  its  interior,  undoubtedly 
save  the  earth's  crust  from  most  disastrous  consequences. 
The  manner  in  which  the  volcanic  mountains  were  con- 
structed will  be  shown  in  the  chapter  on  the  formation 
of  the  earth.     Volcanoes  are  extinct  or  active^  the  ex- 
tinct being  those   mountains  which,  from  their  shape 
and  composition,  are  known  to  have  been  once  in  oper- 
ation, though  not  since  the  advent  of  man,  and  the  active 
being  those  which  have  been  eruptive  since  his  advent. 
While  some  active  volcanoes  are  continually  active,  most 
of  them  have  seasons  of  eruption,  with  intervals  of  rest 
of  various  lengths.     The  shape  of  a  volcano  is  more  or 
less  conical,  the  cone  being  truncated,  that  is,  without  a 
top.     When  it  is  inactive,  the  cavity  of  the  crater  or 
opening  is  shut  up  with  a  crust  of  solid  lava.     It  is  sup- 
posed that  the  occasion  of  an  eruption  is  the  introduction 
of  water  in  some  way  into  the  interior,  generating  steam. 
The  expansions  of  the  steam  produce  the  earthquakes 
which  so  commonly  precede  an  eruption.     The  steam  at 
length  accumulates  to  such  an  extent  that  it  bursts  the 
solid  cover  of  the  crater,  scattering  its  fragments  and 
dust  aloft,  with  sheets  of  flame,  followed  by  the  overflow 
of  the  lava.     The  steam  which  escapes  forms  above  the 
volcano  a  bright  cloud,  and  with  it  there  are  continual 
discharges  of  lightning,  with  thunder,  the  explanation  of 
which  has  been  found  in  the  fact  that  steam  escaping 
from  a  boiler  has  decidedly  electrical  properties.     The 
dust  and  the  condensed  steam  produce,  of  course,  show- 
ers of  rain  and  mud  in  the  neighborhood.     The  matters 
thrown  out  from  a  volcano  are  various  in  their  charac- 
ter.    When  the  eruption  is  about  to  terminate  showers 
of  cinders  fall,  and  the  last  of  the  eruption  is  a  mixture 
of  smoke  and  vapor. 

195.  Vesuvius. — There  is  no  record  of  the  action  of 


112  GEOLOGY. 

this  volcano  previous  to  the  Christian  era,  although  it 
had  the  structure  of  a  volcanic  mountain.  It  had  been 
so  long  inactive  that  vines  grew  all  over  the  interior  of 
the  crater.  In  A.D.  79,  after  a  series  of  shocks  during  a 
dozen  years  previous,  an  eruption  occurred  which  buried 
up  the  cities  of  Herculaneum  and  Pompeii.  There  was 
not  much  lava  thrown  out  in  this  eruption,  but  chiefly 
loose  material,  such  as  sand,  ashes,  cinders,  and  stones. 
The  steam  which  rose  at  the  same  time  from  the  volca- 
no, being  condensed  in  the  air,  fell  in  showers,  and,  be- 
ing mingled  with  the  ashes  and  sand,  currents  of  mud 
ran  into  the  streets,  houses,  and  cellars,  filling  them  up. 
"  Hence  it  is,"  says  Hitchcock,  "  that  when  these  cities 
were  first  excavated,  more  than  a  hundred  years  ago,  ev- 
ery thing  enveloped  was  in  a  most  perfect  state  of  pres- 
ervation— the  pavements  of  lava,  with  deep  ruts  worn  by 
the  carriage  wheels ;  the  names  of  their  owners  over  the 
doors  of  the  houses  ;  the  frescoed  paintings  as  bright  as 
though  put  on  but  yesterday ;  fabrics  in  the  shops  still 
showing  their  texture  ;  vessels  of  fruit  so  well  preserved 
as  to  be  easily  recognized ;  bread  retaining  the  stamp  of 
the  baker,  and  medicine  yet  remaining  on  the  apotheca- 
ry's counter.  The  whole  constitute  perfect  examples  of 
fossil  cities."  Some  skeletons  have  been  found  incased 
in  tuff  or  tufa  (porous  volcanic  rock),  finely  preserved. 
Around  the  neck  of  one  was  a  chain  of  gold,  and  on  the 
bones  of  the  fingers  were  jeweled  rings.  Resina  was  built 
over  the  buried  Herculaneum,  but  this  was  destroyed  by 
a  river  of  lava  in  1631.  In  Fig.  44  you  have  represented 
the  appearance  of  the  crater  of  Vesuvius  in  1829.  The 
top  of  the  volcano  was  blown  off  in  1822  to  the  extent 
of  more  than  800  feet* 

196.  Etna. — This  volcano,  on  the  island  of  Sicily,  is 
about  90  miles  in  circumference,  and  is  nearly  two  miles 
high.  In  its  eruption  in  1669  its  lava  destroyed  fourteen 
towns  and  villages  before  arriving  at  Catania,  and  thero, 
although  the  wall  was  60  feet  high,  it  accumulated  to 


PRESENT    CHANGES    IN   THE    EARTH.  113 


Fig.  44. 

such  an  extent  as  to  pour  over  it,  and,  after  destroying 
a  part  of  it,  ran  on  a  distance  of  15  miles,  and  then  emp- 
tied into  the  sea.  Mantell  says  of  one  of  Etna's  erup- 
tions, "  If  any  person  could  accurately  fancy  the  effect  of 
500,000  sky-rockets  darting  up  at  once  to  a  height  of 
three  or  four  thousand  feet,  and  then  falling  back  in  the 
shape  of  red  hot-balls,  shells,  and  large  rocks  of  fire,  he 
might  have  an  idea  of  a  single  explosion  of  this  burning 
mountain ;  but  it  is  doubtful  whether  any  imagination 
can  conceive  the  eifect  of  one  hundred  of  such  explosions 
in  the  space  of  five  minutes,  or  of  twelve  hundred  or  more 
in  the  course  of  an  hour,  as  we  saw  them." 

197.  Crater  of  Kilauea. — This  volcano,  which  is  always 
active,  is  on  the  island  of  Hawaii.  It  is  the  most  remark- 
able and  singular  volcano  in  the  world.  It  is  not  a  trun- 
cated cone,  but  a  crater  situated  on  high  land  near  the 


114  GEOLOGY. 

base  of  Mount  Loa.  It  is  a  chasm  eight  miles  in  circum- 
ference, and  situated  in  the  midst  of  another  chasm  still 
greater  in  extent,  that  is  surrounded  by  a  precipice  vary- 
ing from  200  to  400  feet  in  height.  In  the  midst  of  the 
inner  chasm  stand  up  fifty  or  sixty  conical  craters,  many 
of  which  are  continually  in  action.  Rivers  of  melted  lava 
run  about  among  the  craters,  and  red-hot  stones,  with  cin- 
ders and  ashes,  are  sent  up  with  flame  from  those  which 
are  active,  in  some  cases  to  an  immense  height. 

198.  Tomboro, — This  is  a  volcanic  mountain  in  the  isl- 
and ofSumbawa.     Lyell  thus  speaks  of  an  eruption  of  it 
in  1815:  "It  began  on  the  5th  of  April,  and  was  most 
violent  on  the  llth  and  12th,  and  did  not  entirely  cease 
till  July.     The  sound  of  the  explosions  was  heard  in  Su- 
matra, at  the  distance  of  970  geographical  miles  in  a  di- 
rect line,  and  at  Ternate,  in  an  opposite  direction,  at  the 
distance  of  720  miles.    Out  of  a  population  of  12,000,  only 
twenty-six  individuals  survived  on  the  island.     Violent 
whirlwinds  carried  up  men,  horses,  cattle,  and  whatever 
else  came  within  their  influence,  into  the  air;  tore  up  the 
largest  trees  by  their  roots,  and  covered  the  whole  sea 
with  floating  timber.     Great  tracts  of  land  were  covered 
with  lava,  several  streams  of  which,  issuing  from  the  cra- 
ter of  the  Tomboro  Mountains,  reached  the  sea.    So  heavy 
was  the  fall  of  ashes  that  they  broke  into  the  president's 
house  at  Birna,  forty  miles  east  of  the  volcano,  and  ren- 
dered it,  as  well  as  many  other  dwellings  in  town,  unin- 
habitable.   On  the  side  of  Java  the  ashes  were  carried  to 
a  distance  of  300  miles,  and  217  toward  Celebes,  in  suffi- 
cient quantity  to  darken  the  air.     The  floating  cinders  to 
the  windward  of  Sumatra  formed,  on  the  12th  of  April,  a 
mass  two  feet  thick  and  several  miles  in  extent,  through 
which  ships  with  difficulty  forced  their  way.     The  dark- 
ness occasioned  in  the  daytime  by  the  ashes  in  Java  was 
so  profound  that  nothing  equal  to  it  was  ever  witnessed 
in  the  darkest  night." 

199.  Graham's  Island. — This  island  rose  up  out  of  the 


PRESENT    CHANGES    IN    THE    EARTH. 


115 


sea  off  the  island  of  Sicily  in  the  year  1831.     Fig.  44,  a, 
represents  it  as  it  appeared  on  the  18th  of  July.     On  the 


Fig.  44,  a. 

4th  of  August  it  appeared  as  seen  in  Fig.  44,  b  (p.  116). 
It  was  180  feet  high,  and  over  a  mile  in  circumference. 
It  was  composed  mostly  of  loose  material,  and  therefore 
was  so  far  washed  away  by  the  water  in  the  course  of 
two  or  three  years  that  there  was  nothing  left  but  a  rocky 
shoal.  Many  other  islands  have  been  seen  to  rise  out  of 
the  sea,  and  there  are  also  many  which  are  composed  of 
lava,  showing  that  they  were  produced,  we  know  not 


116  GEOLOGY. 


Fig.  44,  6. 

when,  by  volcanic  action.  There  is  a  group  of  such  isl- 
ands in  the  Grecian  Archipelago,  the  advent  of  some  of 
which  is  indeed  known.  A  new  island  was  thrown  up 
near  Iceland  in  1783,  consisting  of  high  cliffs,  and  from 
various  parts  of  it  there  were  emitted  fire,  smoke,  and 
pumice.  This  island  was  taken  formal  possession  of  by 
his  Danish  majesty,  but  before  a  year  had  passed  there 
was  nothing  left  to  show  where  it  was  but  a  reef  of 
rocks. 

200.  Earthquakes. — As  earthquakes  very  generally 
precede  an  eruption  of  a  volcano,  and  cease  when  the 
lava  pours  forth,  the  conclusion  is  legitimately  arrived  at 
that  all  earthquakes  are  caused  principally  by  the  move- 
ments of  pent-up  volcanic  matter.  When  they  occur  at 
a  considerable  distance  from  volcanoes,  they  are  owing 
to  heavings  of  that  vast  body  of  melted  matter  which  is 
contained  in  the  interior  of  the  earth  ;  and  it  has  been 
observed  in  such  cases  that,  when  there  has  been  a  suc- 
cession of  earthquakes,  they  have  ceased  when  some  vol- 
cano has,  by  its  eruption,  relieved  the  pressure,  or  when 
some  earthquake  of  great  violence  has  had  the  same 
effect.  Thus,  in  1811,  there  were  many  earthquakes  in 
South  Carolina,  which  ceased  altogether  when  Caraccas 


PRESENT   CHANGES   IN   THE   EARTH.  117 

and  Laguyra,  in  South  America,  were  destroyed.  Anoth- 
er cause  of  earthquakes  has  been  supposed  to  be  a  bend- 
ing in  the  earth's  crust,  arising  from  changes  of  tempera- 
ture. On  this  point  Professor  Dana  gives  the  following 
familiar  illustrations :  "  All  are  familiar  with  the  cracking 
sounds  occurring  at  intervals  in  a  board  floor  of  a  house, 
and  arising  from  change  of  temperature,  especially  in  a 
room  in  winter  that  is  heated  during  the  day ;  and  with 
the  more  common  sounds  of  similar  character  from  the 
jointed  metallic  pipe  of  a  stove  or  furnace,  given  out  aft- 
er a  fire  is  just  made,  or  during  its  decline.  In  each  case 
there  is  a  strain  or  tension  accumulating  for  a  while  from 
contraction  or  expansion,  which  relieves  itself  finally  by 
a  movement  or  slip  at  some  point,  though  too  slight  a 
one  to  be  perceived ;  and  the  action  and  effects  are  quite 
analogous  to  those  connected  with  the  lighter  kind  of 
earthquakes."  Besides  the  vibration  or  wave  movement 
produced  in  the  earth  in  an  earthquake,  there  is  also  a 
vastly  more  rapid  vibration,  which  causes  the  sensation 
of  sound.  The  latter  vibration  commonly  extends  much 
farther  than  the  former. 

201.  Effects  of  Earthquakes. — Earthquakes  produce  va- 
rious effects  according  to  their  violence,  extent,  and  ac- 
companying circumstances.  They  are  chiefly  fractures 
of  the  earth's  crust,  sometimes  very  extensive;  displace- 
ments, either  elevations  or  depressions  for  the  most  part ; 
the  draining  of  lakes,  and  the  production  of  new  lakes ; 
the  production  of  waves  in  the  sea,  sometimes  to  a  great 
distance ;  and  the  destruction  of  life  in  fishes  from  the 
mere  shock  that  is  given  to  them.  The  displacements 
and  fractures  often  involve  a  great  destruction  of  human 
life.  In  the  famous  earthquake  at  Lisbon  in  1755,  the 
greater  part  of  the  city  was  thrown  down,  and  60,000 
persons  were  killed.  Some  most  remarkable  elevations 
and  depressions  have  attended  earthquakes.  The  coast 
of  Chili  was  in  1822  raised  three  feet  over  a  space  of 
100,000  square  miles,  an  area  equal  to  half  of  France.  In 


118  GEOLOGY. 

the  year  1772,  while  PapandayaDg,  one  of  the  loftiest  vol- 
canoes in  the  island  of  Java,  was  in  eruption,  the  mount- 
ain, to  the  extent  of  15  miles  in  length  and  6  in  width, 
fell  in  with  all  its  inhabitants,  and  wholly  disappeared. 

202.  Solfataras. — There  are  localities  in  the  neighbor- 
hood of  volcanoes,  or  where  volcanoes  formerly  existed, 
from  which  sulphur  vapors  arise,  and  result  in  incrusta- 
tions of  sulphur.     Carbonic  acid  gas  also  often  escapes 
from  the  action  of  some  acid,  as  the  sulphuric,  upon  car- 
bonate of  lime  or  limestone. 

203.  Geysers. — Hot  springs  are  very  apt  to  occur  in 
volcanic  neighborhoods,  and  when  they  are  found  where 
there  are  no  volcanoes,  as  in  Virginia,  there  is  evidence 
in  the  character  of  the  rocks  that  volcanic  action  has 
been  present  at  some  time  in  the  past.     The  famous  hot 
springs  of  Iceland  are  called  geysers.     In  the  Great  Gey- 
ser (Fig.  45)  we  have,  in  a  mound  of  silicious  rock,  a  ba- 
sin-shaped cavity  about  fifty  feet  in  diameter.    From  this 
cavity  there  goes  down  perpendicularly  into  the  earth  a 
pipe  some  eight  or  ten  feet  in  diameter  to  the  depth  of 
seventy-eight  feet ;  and  in  the  eruptions  of  the  geyser 
there  issues  from  this  a  huge  column  of  water  to  the 
height  of  150,  sometimes  200  feet.    As  the  water  mounts 
up  it  is  divided  into  numberless  jets,  and  descends  in 
the  form  of  spray,  making  an  immense  and  splendid 
fountain.     The  basin  is  sometimes  empty,  but  is  usually 
filled  with  beautifully  transparent  water,  boiling  brisk- 
ly.    When  the  boiling  is  violent,  and  especially  when 
the  issuing  stream  throws  up  the  water,  subterranean 
noises  are  heard  like  the  booming  of  distant  cannon,  and 
the  earth  is  slightly  shaken.     Each  eruption  is  termina- 
ted by  a  column  of  steam,  which  shoots  upward  with  a 
thundering  noise.     The  hot  water,  from  causes  alluded 
to  in  §  116,  dissolves  some  of  the  silica  in  the  rocks 
within,  and  as  it  falls  deposits  this,  and  thus  forms  the 
mound.     Much  of  the  silicious  matter  is  also  deposited 
in  the  region  round  about,  the  moisture  being  diffused 


PRESENT   CHANGES    IN   THE   EARTH. 


119 


Fig.  45. 

by  the  winds  blowing  upon  the  descending  spray.  Wood 
is  often  found  in  the  neighborhood  petrified  from  this 
cause. 

204.  Explanation. — The  action  of  the  geyser  is  inter- 
mittent, and  its  explanation  has  been  thus  given  by  Ly- 
ell :  "  Suppose  water  percolating  from  the  surface  of  the 
earth  to  penetrate  into  the  subterranean  cavity  A  D 
(Fig.  46,  p.  120)  by  the  fissures  F  F,  while  at  the  same 
time  steam  at  an  extremely  high  temperature,  such  as  is 
commonly  given  out  from  the  vents  of  lava  currents 
during  their  solidification,  emanates  from  the  fissures  C 


120 


GEOLOGY. 


Fig.  46. 


C.  A  portion  of  the  steam 
is  at  first  condensed  into 
water,  while  the  tempera- 
ture of  the  water  is  eleva- 
ted by  the  latent  heat  thus 
evolved,  till  at  last  the  low- 
er part  of  the  cavity  is  filled 
with  boiling  water,  and  the 
upper  part  with  steam  un- 
der high  pressure.  The  ex- 
pansive force  of  the  steam 
becomes  at  length  so  great 
that  the  water  is  forced  up  the  fissure  or  pipe  E  B,  and. 
runs  over  the  rim  of  the  basin.  When  the  pressure  is 
thus  diminished,  the  steam  in  the  upper  part  of  the  cav- 
ity A  expands  until  all  the  water,  D,  is  driven  into  the 
pipe;  and  when  this  happens,  the  steam, being  the  light- 
er of  the  two  fluids,  rushes  up  through  the  water  with 
great  velocity.  If  the  pipe  be  choked  up,  even  for  a 
few  minutes,  a  great  increase  of  heat  must  take  place ; 
for  it  is  prevented  from  escaping  in  a  latent  form  in 
steam, 'so  that  the  water  is  made  to  boil  more  violently, 
and  this  brings  on  an  eruption." 

205.  Sand  Moved  by  Wind.  —  In  some  parts  of  the 
world  great  changes  are  effected  by  clouds  of  sand. 
The  sand-hills  produced  in  this  way  are  called  dunes  or 
downs.  Very  commonly  they  come  from  sand  that  has 
been  washed  up  upon  the  shore  by  the  sea,  which,  on 
being  dried,  is  carried  inland  by  the  winds.  There  are 
many  dunes  of  this  kind  in  Cornwall,  England,  and  on 
the  coast  of  France  a  great  number  of  villages  have  been 
entirely  destroyed  by  them.  They  are  quite  common  on 
some  parts  of  the  coast  of  the  United  States,  and  espe- 
cially on  Cape  Cod.  Sometimes  dunes  occur  in  the  inte- 
rior of  a  country.  In  Egypt  the  westerly  winds  have 
blown  the  sand  over  almost  the  whole  of  the  country 
west  of  the  Nile,  making  it  a  desert,  and  the  remains  of 


PRESENT    CHANGES    IN    THE    EARTH. 


121 


ancient  cities,  with  their  temples  and  palaces,  are  found 
covered  in  the  sand. 

206.  Alteration  of  Levels.  —  Besides  the  depressions 
and  elevations  which,  as  you  have  seen,  have  been  pro- 
duced violently  and  suddenly  by  earthquakes,  there  are 
other  changes  of  a  similar  character  which  have  been 
very  gradual.  There  is  ample  proof  that  in  Sweden 
there  have  been  extensive  alternate  elevations  and  de- 
pressions, which  have  gone  on  so  slowly  that  no  disturb- 
ances have  resulted.  One  of  the  most  interesting  evi- 
dences of  change  of  level  is  found  in  the  pillars  of  what 
has  been  supposed  to  be  the  Temple  of  Jupiter  Serapis, 
near  Naples.  They  are  represented  in  Fig.  47.  You 


i  ig.  47. 


see  some  way  up  the  pillars  a  roughness  of  the  surface. 
This  results  from  a  collection  of  just  such  perforations 
as  are  known  to  be  made  by  certain  sea  mollusks  called 

F 


122  GEOLOGY. 

lithodomes,  the  name  coining  from  two  Greek  words, 
lithos,  stone,  and  domos,  house,  as  these  animals  dwell 
in  the  holes  which  they  make  in  the  stone.  This  shows 
that  the  pillars  were  once,  for  a  considerable  time,  im- 
mersed in  the  sea  as  far  as  the  upper  limit  of  the  rough- 
ness, which  is  23  feet.  Here,  then,  was  a  depression  of 
the  land,  after  the  temple  was  built,  to  a  depth  of  over 
23  feet,  and  it  was  effected  so  gradually  that  the  pillars 
were  left  quietly  standing.  The  subsequent  elevation 
must  have  occurred  with  the  same  slowness  also.  The 
fact  that  Scotland  has  been  raised  up  from  15  to  30  feet 
since  man  came  upon  the  scene  is  very  beautifully  dem- 
onstrated by  Hugh  Miller  in  his  Lectures  on  Geology. 
The  old  coast-lines  have  been  traced  by  him  lying  above 
the  present  coast-lines,  the  identity  between  them,  he  re- 
marks, being  as  decided  as  that  "  between  two  contigu- 
ous steps  of  a  stair,  covered,  the  one  by  a  patch  of 
brown  and  the  other  by  a  patch  of  green,  in  the  pattern 
of  the  stair-carpet."  One  of  the  most  extensive  and  re- 
markable of  the  gradual  changes  of  level  that  have  taken 
place  has  been  observed  in  Sweden  and  Norway.  The 
evidences  of  it  having  been  long  noticed  in  a  rude  way 
by  fishermen  and  pilots,  men  of  science  at  length  under- 
took the  investigation  of  it  systematically,  by  marking 
the  rocks  in  different  places,  and  observing  them  from 
time  to  time.  In  this  way  it  has  been  ascertained  that 
there  is  a  rising  of  the  land  in  the  northern  part  of  this 
region,  and  a  sinking  of  it  in  the  southern  part,  and  the 
rate  is  such  at  some  places  that  the  movement  would 
amount  to  several  feet  in  a  century.  And  that  this 
movement  has  been  going  on  for  many  centuries  is 
shown  by  the  fact  that  such  shells  as  are  now  common 
in  the  Baltic  Sea  are  found  inland,  beginning  at  the  shore 
all  along  up  to  even  400  feet  above  the  level  of  the  sea. 
Other  similar  changes  have  been  noticed  in  South  Amer- 
ica, in  Greenland,  and  in  other  countries. 

207.  Organic  Agencies.— Rocks  are  continually  form- 


CONSTRUCTION    OF   THE   EARTH.  123 

ing  to  a  large  extent  from  material  provided  by  organic 
agencies — that  is,  by  the  agency  of  animals  and  vegeta- 
bles, especially  the  former.  For  example,  the  carbonate 
of  lime  that  is  dissolved  in  water  is  taken  up  by  animals 
• — coral  animals,  shell-fish,  etc.,  and,  forming  their  frame- 
work— their  skeleton,  as  we  may  term  it — is  afterward 
deposited  as  mineral  matter,  becoming  again,  as  it  wa,s 
originally,  a  part  of  the  solid  substance  of  the  crust  of 
the  earth. 

208.  Alterations  made  by  Man. — Wherever  man  fixes 
his  habitation  he  effects  more  or  less  of  change  in  the 
earth's  surface.  These  changes  are  especially  manifest 
in  cities  where  large  bodies  of  men  are  congregated. 
Here  levels  are  often  considerably  altered,  as  may  be 
learned  from  the  recollections  of  the  oldest  inhabitants. 
But  all  the  changes  produced  by  man  are  almost  as 
nothing  compared  with  those  which  come  from  the  op- 
erations of  the  natural  causes  that  I  have  noticed  in  this 
chapter. 


CHAPTER  XI. 

CONSTRUCTION    OF   THE   EARTH. 

209.  Stages  in  the  Construction  of  the  Earth. — You  will 
see,  in  the  developments  which  I  shall  make  in  this  and 
the  succeeding  chapters,  that  there  has  been  a  succession 
of  changes,  each  one  occupying  a  long  period  of  time, 
the  earth  being  brought  gradually  into  a  proper  condi- 
tion as  a  habitation  for  man.  You  will  see  that  the  con- 
tinents were  once  mere  germs  of  continents,  and  that 
they  grew  to  be  what  they  are  after  a  manifest  plan,  the 
steps  of  which  the  geologist  has  been  able  to  some  ex- 
tent to  discover  by  his  researches  among  the  rocks.  You 
will  see  that  during  all  this  time  there  was  much  of  tear- 
ing down  and  rebuilding  as  a  part  of  the  plan,  the  sedi- 


124  GEOLOGY. 

mentary  ruins  of  rocks  being  the  materials  out  of  which 
a  large  portion  of  the  rocks  we  now  find  were  construct- 
ed. You  will  see  that,  although  at  the  first  there  were 
ages  in  which  there  was  no  life,  vegetable  or  animal,  there 
was  a  long  series  of  ages  before  man  appeared  in  which 
the  earth  swarmed  with  life,  the  relics  being  found  now 
imbedded  in  the  rocks,  differing  from  each  other,  howev- 
er, in  a  marked  manner,  as  geologists  have  found,  in  the 
different  stages  of  the  earth's  construction.  It  is  from 
these  differences  in  the  forms  of  life  that  geologists  have 
been  able  to  mark  out  the  periods  or  ages  of  the  world's 
formation.  In  the  present  chapter* it  is  my  intention  to 
point  out  some  of  the  processes  by  which  the  earth  has 
been  gradually  built  up  into  its  present  condition,  as  pre- 
paratory to  the  consideration  of  what  took  place  in  each 
of  its  several  ages.  What  you  have  already  learned  of 
the  present  changes  going  on  in  the  earth,  you  will  find, 
will  throw  much  light  upon  this  subject,  because,  as  I 
have  before  stated,  the  same  agents  which  are  at  work 
now  in  these  changes  did  the  work  in  the  changes  of  the 
far  past. 

210.  Nature  of  Geological  Evidence.  —  The  geologist 
takes  the  results  of  processes  which  are  now  going  on  in 
the  earth,  and,  comparing  them  with  the  results  which  he 
finds  buried  up  in  the  rocks,  adopts  his  conclusions  in  re- 
gard to  the  latter,  and  does  so  without  danger  of  error 
if  he  be  properly  cautious.  I  will  give  a  few  illustrations 
of  his  modes  of  reasoning. 

The  geologist  finds  a  rock  which,  on  examination,  is 
discovered  to  be  of  the  same  composition  with  clay,  and, 
more  than  this,  has  similar  layers.  He  infers  that  the 
rock  was  once  clay,  and  in  some  way  became  solidified 
or  changed  into  rock.  By  the  same  reasoning  he  infers 
that  certain  rocks  were  once  mud,  and  certain  others 
were  once  sand.  The  inference  in  these  cases  is  con- 
firmed by  the  fact  that  the  solidification  has  sometimes 
been  known  to  take  place  within  a  short  period  of  time, 


CONSTRUCTION    OF   THE    EARTH.  125 

as  you  have  already  seen  in  §  180,  and  will  see  more  fully 
hereafter. 

The  geologist  finds  a  rock  which  contains  imbedded  in 
it  certain  shells.  These  shells  were,  like  the  shells  we 
now  pick  up  on  the  sea-shore,  once  inhabited  by  animals. 
But  how  did  they  get  into  the  rock?  This  question  is 
easily  solved  by  the  geologist.  He  finds  shells  at  the 
present  time  imbedded  in  mud  or  sand,  the  mineral  char- 
acter of  which  is  precisely  the  same  with  that  of  the  solid 
rock  containing  the  other  shells.  He  then  justly  infers 
that  the  latter  were  once  in  similar  mud  or  sand,  which 
is  now  solidified. 

He  makes  a  farther  inference  in  regard  to  this  rock  by 
comparison  with  some  other.  Some  of  its  shells  may  be 
of  the  same  species  with  some  that  are  found  at  the  pres- 
ent day,  while  those  found  in  the  rock  with  which  it  is 
compared  may  all  be  different  from  any  of  the  present 
species.  His  inference  is  that  the  latter  rock  belongs  to 
an  earlier  age  than  the  former.  It  may  have  been  made 
or  solidified  into  rock  hundreds,  or  even  thousands  of 
centuries  before  the  other,  though  the  two  may  now  lie 
in  juxtaposition.  The  kind  of  observation  here  indicated, 
you  will  find  as  we  proceed,  is  largely  made  use  of  in  de- 
termining the  relative  ages  of  rocks ;  for  as,  during  al- 
most all  the  ages  of  the  earth,  there  have  been  living  be- 
ings, but  differing  in  character  from  age  to  age,  the  re- 
mains of  life  found  in  the  rocks  differ  according  to  the 
ages  in  which  the  rocks  were  formed. 

Take  another  case.  You  often  see  in  a  block  of  sand- 
stone— a  step  perhaps  at  some  door — pebbles  imbedded 
in  the  material  of  which  most  of  the  rock  was  made. 
These  pebbles  are  such  as  you  have  seen  on  a  shore,  and 
you  know  that  they  once  were  rough  pieces  of  rock,  and 
that  they  were  smoothed  by  being  rubbed  together  along 
time,  as  those  you  see  on  the  shore  have  been,  by  water 
rushing  over  them,  and  that  after  this  was  done  they  be- 
came mingled  with  sand,  and  the  whole  became  a  solid 


126  GEOLOGY. 

rock.  This  pudding-stone,  as  it  is  called,  we  can  make 
such  inferences  about  just  as  clearly  as  we  can  infer  the 
mode  of  making  a  plum-pudding  from  its  appearance. 

The  geologist  goes  much  farther  than  this.  He  dis- 
covers often  in  the  layers  of  rock  tracks,  and  even  the 
marks  of  rain-drops  and  ripples,  made  perhaps  ages  upon 
ages  ago.  I  will  give  a  single  example.  Professor  Dana 
says  of  some  slabs  examined  in  Pottsville,  Pennsylvania, 
"We  thus  learn  that  there  existed  in  the  region  about 
Pottsville  at  that  time  (a  period  just  before  the  coal  of 
that  region  was  deposited)  a  mud  flat  on  the  border  of  a 
body  of  water ;  that  the  flat  had  been  swept  by  wavelets, 
leaving  ripple  marks ;  that  the  ripples  were  still  fresh 
when  a  large  amphibian  walked  across  the  place ;  that  a 
brief  shower  of  rain  followed,  dotting  with  its  drops  the 
half-dried  mud;  that  the  waters  again  flowed  over  the 
flat,  making  new  deposits  of  detritus,*  and  so  buried  the 
records." 

211.  Classes  of  Rocks. — First,  rocks  are  divided  into 
two  grand  classes,  the  stratified  and  the  unstratified. 
The  stratified  appear  in  strata  or  layers,  and  the  surfaces 
of  these  strata  are  nearly  or  quite  parallel.  They  are 
either  earthy  aggregates,  as  sandstones,  or  simple  chemi- 
cal precipitates  from  solutions,  as  the  limestones  some- 
times are.  Those  which  are  mere  aggregates  were  de- 
posited as  sediment,  and  therefore  are  called  sedimentary 
rocks.  They  are  also  called  aqueous  rocks,  as  are  also 
those  which  were  precipitated,  because  water  was  the 
agent  by  which  the  matter  composing  them  was  brought 
to  the  locality  and  deposited.  You  have  an  example  of 
stratified  rock  in  Fig.  48.  Stratified  rocks  very  general- 
ly contain  fossils — that  is,  remains  of  plants  and  animals 
which  were  in  existence  at  the  time  that  the  material  of 
which  they  are  composed  was  deposited,  and  are  therc- 

*  This  term  is  applied  to  what  has  been  removed  from  the  surfaces 
of  rocks  by  the  erosion  of  water  and  other  causes.  When  the  material 
thus  removed  is  coarse,  it  is  called  debris. 


CONSTRUCTION    OF   THE    EARTH. 


327 


Fig.  48. 

fore  called  fossiliferous  rocks.  Metamorphic  rocks  are 
stratified  rocks  which  have  been  changed  by  the  action  of 
heat,  and  perhaps  some  other  auxiliary  agencies.  In  this 
alteration,  any  fossils  that  the  rocks  originally  contained 
are  obliterated,  the  material  which  composed  them  hav- 
ing been  altered  with  the  rest  of  the  rock  in  the  arrange- 
ment of  its  particles.  Thus  limestone  containing  shells 
and  corals  has  been  often  converted  into  granular  lime- 
stone or  marble,  a  crystalline  texture  being  thus  given  to 
the  whole.  The  term  metamorphism  means  transforma- 
tion, and  comes  from  two  Greek  words,  meta,  which  is 
the  same  as  trans  in  the  Latin,  and  morplie,  form.  A 
very  decisive  proof  that  heat  is  the  principal  cause  of 
metamorphism  we  have  in  the  fact  that  great  artificial 
heat,  if  long  continued,  changes  the  structure  of  stones. 
Sandstone  used  in  furnaces  has  sometimes  been  known 
to  become  crystalline — that  is,  has  been  metamorphosed. 
The  unstratified  rocks  are  not  divided  into  parallel  lay- 
ers, but  they  are  commonly  a  shapeless  mass,  as  seen  in 
Fig.  49  (p.  128).  They  were  not  deposited  from  sedi- 
ment, but  were  formed  under  the  influence  of  heat,  and 
were  thrust  up  from  within  the  crust  of  the  earth.  They, 
of  course,  never  have  any  fossils  in  them.  They  general- 


128  GEOLOGY. 


Fig.  40. 

ly  appear  in  mountains,  forming  often  their  central  part, 
while  the  stratified  abound  in  plains,  or  flank  the  sides 
of  the  mountains.  When  a  mass  of  unstratified  rock,  as 
granite,  stands  up  as  the  axis  or  central  part  of  a  mount- 
ain, stratified  rocks  commonly  slope  off  from  the  granite, 
this  having  thrust  them  to  the  one  side  and  the  other  as 
it  rose  up  out  of  the  bowels  of  the  earth. 

There  is  one  class  of  unstratified  rocks,  the  trappean, 
noticed  in  §  152,  which  have  a  tendency  to  regularity  of 
shape,  and  in  some  cases  the  tendency  is  fully  carried 
out.  In  this  they  are  distinguished  from  the  shapeless 
masses  of  granite  and  other  unstratified  rocks. 

212.  Stratification,  Lamination,  Joints,  and  Cleavage. — 
The  word  layer  is  often  used  as  meaning  the  same  thing 
as  stratum,  but  in  the  strict  use  of  the  latter  term  it  in- 
cludes all  the  layers  of  the  same  kind  which  are  next  to 
each  other.  A  stratification  means  a  succession  of  lay- 
ers, either  of  the  same  kind  or  of  different  kinds.  Lay- 
ers differ  very  much  in  thickness,  according  to  the  man- 
ner in  which  they  were  laid  down.  When  they  are  very 
thin  they  are  called  laminae.  In  shales  and  micaceous 
sandstones  the  Iamina3  are  so  thin  that  we  may  properly 
speak  of  them  as  films,  and  it  is  plain  that  in  such  cases 
the  stratum  or  bed  was  formed  by  the  very  gradual  ac- 
cumulation of  films  of  clay  or  of  micaceous  spangles, 
which  settled  down  at  the  bottom  of  comparatively  still 


CONSTRUCTION    OF    THE   EARTH.  129 

water.  Each  film  or  lamina  was  the  result,  of  course,  of 
a  separate  deposition — that  is,  after  each  lamina  was 
completed,  there  was  a  pause  for  a  time  in  the  deposi- 
tion from  the  water.  In  those  cases  in  which  there  are 
fifty,  or  even  a  hundred  laminae  in  the  thickness  of  an 
inch,  the  process,  including  the  intervals,  must  have  been 
very  slow.  Some  years  must  have  been  required  to  lay 
down  a  foot  of  such  a  bed.  Where  the  lamination  is  not 
so  fine,  the  accumulation  of  the  sediment  of  which  the 
rock  was  made  was  more  rapid.  The  term  formation  is 
applied  to  a  series  of  strata  that  have  a  relation  to  each 
other  in  similarity  of  fossils,  and  which  are  therefore  in- 
cluded in  the  same  age  or  period.  This  is  the  general 
idea,  but  the  word  is  used  rather  loosely,  being  made  to 
refer  to  a  larger  range  of  strata  at  one  time  than  at  an 
other.  In  looking  at  a  stratified  rock,  you  observe  be- 
side the  horizontal  lines  which  indicate  the  divisions  be- 
tween the  layers  certain  lines  which  cross  these.  The 
two  sets  of  lines  are  seen  in  Fig.  50.  The  lines  which 


Fig.  50. 

run  up  and  down  across  the  layers  indicate  planes  of  di- 
vision, which  are  called  joints.  Some  of  thesej  you  see, 
extend  farther  than  others,  and  these  are  called  master- 
joints.  There  are  commonly  two  sets  of  joints  at  right 
angles  to  each  other,  as  is  represented  in  the  figure.  It 

F2 


130  GEOLOGY. 

is  this  arrangement  that  enables  the  workman  to  get  out 
readily  square,  or,  rather,  squarish  blocks  of  stone.  The 
regularity  of  these  divisions  varies  much  in  different 
cases.  Sometimes  it  is  so  great  that  the  upper  surface 
of  a  stratum  has  very  much  the  appearance  of  a  regular 
pavement  made  with  nicely-fitted  slabs.  Where,  from 
any  cause,  the  rocks  are  occasionally  thrown  down,  ex- 
posing new  surfaces  of  the  strata  with  their  joints,  there 
is  a  resemblance  to  the  ruins  of  fortifications.  In  Fig. 
51  we  have  a  view  of  some  of  the  clifis  of  Cayuga  Lake, 


Fig.  51. 


K.  Y.,  which  weathering  and  the  undermining  action  of 
the  water  are  continually  wearing  away,  so  that  fresh 
surfaces  show  in  very  definite  manner  the  planes  and 
lines  of  division.  Cleavage^  or  the  slaty  structure,  is  an- 
other kind  of  division  in  rocks.  This  is  sometimes  par- 
allel with  the  layers,  and  sometimes  runs  across  them. 
Both  the  larger  divisions  by  joints,  and  the  smaller  ones 
by  cleavage,  each  often  extend  over  vast  regions  of 
country  at  the  same  angle,  showing  that  some  causes 
operating  extensively  produce  them. 

213.  Order  of  Succession  of  Rocks. — There  is  a  regu- 
lar order  in  the  stratified  rocks  which  is  never  trans- 


CONSTRUCTION    OF   THE   EARTH. 


131 


gressed,  so  that  the  geologist  can  apply  conclusions 
made  in  regard  to  rocks  in  one  quarter  of  the  world  to 
those  which  exist  in  any  other  quarter.  There  may  be 
omissions,  but  there  is  never  any  change  in  the  order. 
"As  a  bookbinder,"  says  Phillips,  "sometimes  neglects 
to  bind  in  a  particular  leaf,  so  Nature  sometimes  omits  a 
particular  rock ;  but  she  never  misplaces  the  rocks,  as 
the  careless  workman  sometimes  misplaces  the  pages." 
There  is  a  very  signal  example  of  such  an  omission  in 
the  rocks  of  this  country.  We  have  here  the  cretaceous 
or  chalk  formation — that  is,  the  series  of  rocks  so  called; 
but  the  chalk,  which  forms  so  prominent  a  part  of  this 
series  in  England,  France,  and  many  other  countries,  is 
wholly  absent ;  that  leaf  in  the  American  geological  vol- 
ume is  left  out. 

214.  Flexures  of  Strata. — Though  strata  are  deposited 
generally  either  horizontally  or  nearly  so,  they  are  often 
very  much  bent,  as  is  represented  in  Fig.  52.  There  are 


Fig.  52. 

some  magnificent  exhibitions  of  these  flexures  in  some 
of  the  mountainous  regions.  Among  the  Alps  there  are 
mountains  thousands  of  feet  high,  looking,  as  Professor 
Hitchcock  says,  "  as  if  crumpled  together  by  some  migh- 
ty hand."  It  would  seem  as  if  it  were  not  possible 
thus  to  bend  rocky  strata  without  breaking  them.  But 
probably  the  rocks  were  both  moistened  and  heated 
when  this  was  done.  Besides,  the  bending  force  un- 
doubtedly was  made  to  act  very  gradually.  Some  light 
is  thrown  on  this  point  by  some  observations  in  regard  to 
the  bending  of  ice.  Though  ice  is  a  very  brittle  solid, 


132 


GEOLOGY. 


large  blocks  of  it  have  been  known  gradually  to  bend 
very  considerably.  Kane  saw  this  in  a  flat  block  of  ice 
eight  feet  thick,  and  twenty  or  more  wide,  supported 
only  at  its  two  ends.  In  the  course  of  two  months  it 
became  so  much  bent  that  the  middle  of  it  was  depressed 
five  feet. 

215.  How  the  Flexures  are  Produced. — It  is  supposed 
that  the  flexures  of  the  strata  were  produced  by  lateral 
pressure.     This  has  been  illustrated  by  a  simple  experi- 
ment by  Sir  James    Hall.     He  took 
pieces  of  cloth,  some  linen  and  some 
woolen,  and,  placing  them  in  layers  on 
a  table  (Fig.  53),  compressed  them  by 
the  weight  a.     He  then  applied  press- 
ure to  the  sides  b  b, 

as  shown  in  Fig.  54, 

and  found  that  while 

the  weight  a  was 
raised,  the  layers  of  cloth  were  bent 
in  folds  like  those  which  are  seen  in 
layers  of  rock  in  nature.  Sir  C.  Lyell 
observed  a  result  near  Boston  which 
well  illustrates  the  action  of  this  later- 
al pressure.  For  the  purpose  of  con- 
verting part  of  an  estuary,  overflowed  at  high  tide,  into 
dry  land,  a  vast  quantity  of  stones  and  sand  was  thrown 
into  it.  The  eflect  of  this  was  to  push  up  the  bottom 
of  the  estuary  alongside  of  this  load  of  stones  and  sand, 
so  that  it,  in  the  course  of  a  few  months,  was  raised 
six  feet  above  high-water  mark,  and  some  five  or  six 
folds  were  produced  in  it,  just  like  the  folds,  small  and 
great,  which  the  geologist  finds  in  rocky  strata. 

216.  Upheavals  of  Strata,  with  Fracture.— Fig.  55  is  a 


Fig.  53. 


Fig.  54. 


Fig.  55. 


CONSTRUCTION    OF   THE   EARTH. 


133 


representation  of  such  an  upheaval.  Fissures  of  various 
dimensions,  sometimes  of  immense  size,  are  made  in  this 
way,  and  this  is  the  origin  of  many  of  the  valleys  which 
we  see  with  steep,  bold  sides.  Chasms  and  caverns  are 
produced  by  such  upheavals ;  water,  by  its  erosive  agen- 
cy, acting,  however,  at  the  same  time,  and  afterward  in 
many  cases,  especially  where  there  are  caverns  of  consid- 
erable extent.  Natural  bridges  are  the  result  of  up- 
heavals, an  example  of  which  is  given  in  Fig.  56,  repre- 
senting that  of  Icononzo,  in  South  America. 


Fig.  56. 

217.  Strata  at  different  Angles. — One  consequence  of 
upheavals  with  fracture  is  that  we  have  strata  lying  at 
different  angles,  as  is  often  shown  when  their  projecting 
ends  or  sides  are  laid  bare.  The  order  of  the  rocks  is 
thus  brought  to  view  sometimes  to  a  great  extent,  as  in 
the  case  of  Snake  Mountain,  in  Vermont,  represented  in 
Fig.  57  (p.  134).  The  place  of  fracture  is  at  c,  and  there 
is  brown  clay  at  e,  extending  from  here  west  six  miles  to 
Lake  Champlain,  and  lying  upon  n,  limestone  rock.  I 
will  trace  the  layers  of  rock  up  the  mountain.  At  b  we 


134 


GEOLOGY. 


Fig.  57. 

have  sand  rock,  at  d  one  kind  of  limestone,  at  a  another 
kind,  and  the  same  as  that  on  which  the  brown  clay,  6, 
lies ;  at  g  is  slate  rock,  at  h  are  shales,  and  at  I  red  sand 
rock ;  at  k  is  debris  from  the  sand  rock,  Z,  and  at  i  is  a 
cranberry  meadow  lying  on  peat.  Sometimes  the  strata 
in  the  upheaval  become  vertical,  as  seen  in  Fig  58,  which 
is  a  representation  of  vertical 
strata  on  which  a  castle  has 
been  built.  These  strata  were 
laid  down  horizontally  far  back 
in  the  past,  ages  upon  ages  be- 
fore man  was  introduced,  and 
then  by  some  mighty  upheaval 
were  raised  to  their  present  po- 
sition. Sometimes  strata  appear  to  be  horizontal  when 
they  are  very  far  from  it.  Take  such  a  case  as  that  pre- 


i'ig.  58. 


Fig.  59. 


sen  ted  in  Fig.  59.     If  the  spectator  were  in  the  vessel,  so 
as  to  look  at  the  rocks  as  they  appear  on  the  side p,  the 


CONSTRUCTION    OF   THE   EARTH. 


135 


strata  would  appear  to  be  horizontal,  when  in  reality  they 
lie  at  an  angle  of  about  45°,  and  gradually  become  verti- 
cal as  you  go  toward  a. 

218.  Dip  and  Strike. — These  are  terms  which  are  much 
used  in  geology,  and  therefore  require  explanation.  The 
line  of  variation  of  strata  from  a  horizontal  line  is  called 
their  dip.  For  example,  in  the  case  shown  in  Fig.  60,  if 

the  angle  made 
by  the  lines  of 
the  strata,  b  #, 
with  the  hori- 

-  60.  zontal  line,  a,  be 

45  degrees,  these  strata  are  said  to  dip  45  degrees.  The 
strike,  on  the  other  hand,  is  the  line  of  direction  in  which 
the  edges  of  the  strata  run.  The  meaning  of  these  terms 
can  be  made  clear  by  a  simple  illustra- 
tion. If  you  place  a  book  on  the  ta- 
ble, as  seen  in  Fig.  61,  with  the  edges 
of  the  leaves  downward,  and  move 
one  side  of  the  cover  away  from  the 
body  of  the  book,  a  line  from  the  back 
of  the  book  straight  down  the  cover, 
#,  will  be  the  line  of  dip,  while  a  line 
along  the  back  of  the  book,  a  a,  will 


Fig.  61. 

be  the  line  of  strike. 


219.  Anticlinal  and  Synclinal  Lines.  —  An  anticlinal 
line  is  a  line  along  which  the  strata  dip  in  opposite  di- 
rections. This  may  be  exemplified  by  placing  the  book 
in  the  position  seen  in  Fig.  62.  The 
line  along  the  back  of  the  book  repre- 
sents the  anticlinal  line.  The  syncli- 
nal line  is  the  reverse  of  this.  To  rep- 
resent it,  let  the  book  be  placed  in  the 
position  seen  in  Fig.  63  (p.  136).  The 
line  at  the  angle  of  the  two  parts  of 
the  book  is  the  synclinal  line.  These 
lines  do  not,  however,  run  along  sharp 


Fig.  C2. 


136  GEOLOGY. 

angles,  as  these  illustrations  would  in- 
dicate, but  curves,  and  therefore  anti- 
clinal and  synclinal  curves  are  spoken 
of — in  the  anticlinal  the  sides  inclin- 
ing upward  toward  each  other  like  the 
roof  of  a  house,  but  in  a  curved  line, 
while  the  sides  of  a  synclinal  curve  in- 
cline downward  toward  each  other, 
like  the  sides  of  a  trough. 

220.  Measuring  Strata. — Where  strata  outcrop  we  can 
very  readily  take  the  measurement  of  their  thickness. 
The  manner  in  which  this  is  done  is  so  well  pointed  out 
by  Mr.  Jukes,  Director  of  the  Geological  Survey  of  Ire- 
land, that  I  will  give  you  his  description  of  it  entire : 
"  Having  procured  a  good  map  of  the  district  we  are  go- 
ing to  examine,  a  pocket  compass,  and  a  small  instrument 
called  a  clinometer,  by  which  we  can  determine  the  an- 
gle at  which  a  bed  inclines  from  the  horizontal  plane,  we 
begin  to  look  for  exposures  of  rock.  The  district  may 
perhaps  at  first  appear  to  be  entirely  covered  by  soil  and 
vegetation,  but,  when  thoroughly  examined,  it  may  show 
here  and  there  some  crags  of  bare  rock,  some  bare  cliffs 
on  the  side  of  a  river,  some  cutting  on  a  road-side,  or 
some  quarries.  Let  Fig.  64  be  a  piece  of  our  map  trav- 
ersed by  a  brook  and  a  road,  and  suppose  that  we  find 
some  quarries  of  limestone  in  the  northeast  corner  of  the 
district,  all  the  beds  of  which  dip  to  the  southwest  at  an 
angle  of  20°.  Let  us  represent  these  limestones  by  the 
cross-barred  lines  in  the  northeast  corner  of  the  figure, 
drawing  them  in  a  northwest  and  southeast  direction  to 
represent  their  strike,  and  indicating  their  dip  by  an  ar- 
row with  20°  annexed  to  it.  In  examining  the  banks  of 
the  brook,  suppose  we  find,  in  two  places  lying  in  the 
same  line  of  strike,  some  shales,  represented  by  plain 
close  lines ;  a  bed  of  coal,  represented  by  a  thick  dark 
line;  and  some  sandstones,  represented  by  dots;  and, 
for  simplicity's  sake,  let  us  suppose  them  all  to  dip  south- 


CONSTRUCTION  OF  THE  EARTH. 


137 


Fig.  64. 

west  at  20°.  Then  suppose  that  we  find  one  or  two  oth- 
er detached  exposures  of  sandstone  and  shale  to  the 
southwest  of  the  above,  with  similar  strikes  and  dips. 
And,  lastly,  suppose  that  in  the  southwest  corner  of  the 
district  we  find  some  more  limestone  of  quite  a  different 
kind  from  that  in  the  northeast  corner,  but  still  dipping 
to  the  southwest  at  20°.  It  will  be  obvious  that  these 
limestones  in  the  southwest  corner  of  the  map  lie  above 
all  the  other  rocks,  while  the  limestones  in  the  northeast 
corner  rise  out  from  beneath  all  the  rest." 

221.  Calculating  the  Thickness  of  Strata. — In  the  case 
just  detailed,  we  have  data  for  arriving  at  the  thickness 
of  this  whole  set  of  strata.  The  manner  in  which  this 
is  done  can  be  explained  on  Fig.  65  (p.  138),  which  rep- 
resents a  section  of  the  district  at  right  angles  to  the 
strike  of  the  rocks.  "Suppose,"  says  Mr.  Jukes,  "that 
we  wish  to  sink  a  pit  at  the  part  marked  shaft  in  the 
map,  in  search  of  the  coal,  and  that,  before  commencing, 
we  wish  to  know  how  deep  the  coal  is  there,  and  how 
far  it  is  to  the  limestone  below  it.  We  take  the  map, 


GEOLOGY. 


Fig.  65. 


and  draw  the  line  A  B  from  southwest  to  northeast 
through  the  spot  we  select  for  our  shaft,  and  then,  with 
some  leveling  instrument,  ascertain  the  undulations  of 
the  ground  along  that  line,  taking  the  level  of  the  sea  as 
our  '  datum  line.'  Having  thus  got  the  true  outline  of 
the  ground,  which  we  may  suppose  to  be  given  in  Fig. 
65,  we  draw  lines  inclined  at  an  angle  of  20°  toward  the 
southwest  at  the  several  spots  where  the  section  line  is 
cut  by  the  outcrops  of  the  beds,  or  by  straight  lines  join- 
ing them,  and  this  section  will  then  show  us  the  depth 
at  which  the  shaft  will  reach  any  of  the  beds.  Similar- 
ly, if  we  wish  to  know  the  thickness  of  the  whole  suc- 
cession of  beds,  from  the  highest  to  the  lowest,  of  those 
exposed  in  the  district,  the  length  of  the  line  marked 
thickness  will  give  it  to  us,  when  measured  on  the  scale 
we  adopt  for  our  map  and  section." 

In  these  simple  operations  is  indicated  the  mode  of 
ascertaining  some  great  geological  facts,  for  it  is  by  such 
observations  and  measurements  that  we  gain  a  far  more 
extensive  knowledge  of  the  crust  of  the  earth  than  we 
can  by  the  deepest  mining  excavations;  The  great  up- 
heavals have  turned  up  to  us  the  leaves  of  geological 
history  for  our  reading,  many  of  which  we  could  not 
otherwise  have  read,  for  they  would  have  been  so  deep 
that  no  exploration  of  man  could  have  reached  them. 

222.  Conformable  and  Unconformable  Strata. — Strata 
are  said  to  be  conformable  when  their  surfaces  or  planes 


CONSTRUCTION    OF    THE 


139 


are  parallel  to  each  other.    They  are  unconformable  when 
their  planes  are  not  parallel.     Thus,  in  Fig.  66,  all  the 


Fig.  6G. 

horizontal  strata  a  are  conformable  to  each  other,  and  so 
are  also  the  inclined  strata  b;  but  the  strata  b  have  the 
strata  a  lying  unconformably  upon  them.  All  the  strata 
b  were  deposited  in  a  horizontal  position,  and  there  was 
no  upheaval  till  the  last  of  them  was  completed.  Then 
the  state  of  quiescence  was  broken,  and  the  strata  were 
lifted  up  as  you  see  ;  and  when  the  upheaving  force 
ceased  to  act,  the  upper  horizontal  strata  began  to  be 
deposited.  Periods  of  immense  length  were  required 
for  all  these  successive  processes,  for  the  upheaval  was 
probably  very  slow,  as  the  depositions  certainly  were. 

223.  Faults.  —  Whenever  in  a  fracture  of  strata  there 
occurs  a  dislocation  of  them,  leaving  those  on  one  side 
of  the  fissure  higher  up  than  those  on  the  other,  it  is 
called  a  fault,  a  name  which  was  first  given  to  such  a 

state  of  things  by  miners. 
In  Fig.  67  you  have  a  rep- 
resentation of  a  fault.  The 
strata  marked  with  corre- 
sponding letters  on  each 
side  of  the  fissure  were 
continuous  till  they  were 
all  deposited,  and  then,  by 
some  force,  either  the  stra- 
ta on  the  right  hand  were  depressed,  or  those  on  the  left 
were  elevated.  Faults  vary  much  in  the  degree  of  dis- 
location, from  a  few  feet  up  to  many  thousands.  Some 
of  the  grand  changes  in  the  earth's  crust  have  been  pro- 
duced by  faults. 

224.  Denudation.  —  This  term  is  applied  to  the  wear- 


140  GEOLOGY. 

ing  away  of  rocks  by  flowing  water.  This  erosive  pow- 
er of  water,  spoken  of  in  §  186,  has  produced  some  of 
the  most  immense  changes  that  have  taken  place  in  the 
earth.  You  have  seen  what  vast  quantities  of  material 
it  supplies  to  be  carried  down  by  the  rivers  into  lakes 
and  seas.  The  hills  and  mountains,  though  made  by 
foldings  of  strata  and  upheavals,  generally  received  their 
final  shaping  from  denudation.  Though  erosion  by  wa- 
ter is  comparatively  a  slow  process,  yet,  acting  through 
long  periods,  it  produces  great  effects.  It  is  supposed 
that  the  Appalachian  Mountains  have  lost  from  this 
cause  as  much  material  as  is  now  contained  in  them,  or 
even  more,  and  the  same  can  be  said  of  some  other 
ranges  of  mountains.  Indeed,  in  the  changes  of  the 
long  ages  occupied  by  the  earth's  foundation,  the  great 
majority  of  the  rocks  have  been  built  up  from  materials 
furnished  by  denudation  from  pre-existing  rocks,  and 
often  denudation  and  reconstruction  have  succeeded 
each  other  many  times  over  in  the  case  of  the  same  ma- 
terial. This  same  succession  is  seen  to  a  considerable 
extent  even  now. 

225.  Faults  with  Denudation. — Denudation  has  often 
united  with  faults  in  producing  great  changes.  This 
may  be  illustrated  by  Fig.  68,  representing  a  section  of 


a  coal-field  in  England  of  several  miles  in  extent.  There 
are  four  divisions,  A,  B,  C,  and  D,  made  by  faults  which 
have  put  the  strata  in  them  at  different  relative  depths. 
Thus,  in  A,  the  bed  of  coal,  X,  is  900  feet  from  the  snr- 


CONSTRUCTION  OF  THE  EARTH.          141 

face,  and  has  over  it  various  strata  of  sandstone  and 
shale,  1,  2,  3,  4,  and  5.  In  the  divisions  B  and  D  there 
is  only  the  stratum  5  above  the  coal,  which  is  only  200 
feet  from  the  surface,  while  in  the  division  C  the  coal 
lies  700  feet  deep.  Now,  notwithstanding  this  displace- 
ment of  the  strata,  there  is  no  appearance  of  the  up- 
heavals on  the  surface  of  the  coal-field,  but  that  is  level. 
If  the  material  all  remained  on  the  spot,  we  should  have 
an  uneven  surface,  and  at  O  O  there  would  be  an  eleva- 
tion of  700  feet,  for  that  is  the  amount  of  uplift  in  the 
strata  at  that  part  of  the  field.  The  inference  is  that  all 
this  great  mass  of  material,  indicated  by  the  dotted  line, 
was  removed  by  denudation.  Near  Chambersburg,  Pa., 
there  is  a  fault  20  miles  in  length,  and  the  depth  of  the 
dislocation  is  20,000  feet,  and  yet  a  man  can  stand  with 
one  foot  on  one  side  of  this  fracture  and  the  other  foot 
on  the  other  side.  What  has  become,  then,  of  this  im- 
mense mass  of  material  20,000  feet  in  height  ?  "  It  must 
have  been  swept,"  says  Mr.  Lesley,  who  gives  the  ac- 
count, "into  the  Atlantic  by  the  denuding  flood."  If 
this  had  not  been  done  there  would  have  stood  there  a 
bold  precipice  nearly  four  miles  in  height  and  twenty 
miles  in  length.  Long  ages  must  have  been  required 
for  water  to  effect  such  a  denudation.  The  proximity 
in  which  such  a  fault  places  rocks  of  epochs  far  distant 
from  each  other  bring  to  the  mind  grand  and  over- 
whelming conceptions  of  the  vast  periods  of  time  which 
have  elapsed  in  the  building  up  of  the  world.  On  the 
one  side  of  that  crevice  you  step  on  limestone  that  was 
made  long  ages  before  the  slaty  rock  that  you  step  on 
upon  the  other,  and  by  accident  there  are  lodged  in  that 
crevice  fragments  of  a  rock  of  still  another  epoch  be- 
tween the  epochs  of  those  on  either  side. 

226.  How  Mountains  were  Made. — You  are  now  pre- 
pared to  see  how  mountains  were  built  up.  They  were 
not  all  constructed  and  shaped  in  the  same  way,  but 
there  is  much  variety.  I  Avill  indicate  some  of  the  prin- 


142 


GEOLOGY. 


cipal  modes.  I  have  already  mentioned  the  agency  of 
flexure  or  plication,  as  illustrated  by  Fig.  52.  Denuda- 
tion has  much  to  do  with  the  formation  of  such  mount- 
ains, as  seen  in  Fig.  69.  Here  you  see  on  each  side 


Fig.  69. 

strata  which,  if  continued  on  over  the  mountain,  would 
very  much  increase  its  height ;  but  they  were  removed 
probably  by  the  water  sweeping  over  the  mountain  all 
the  time  that  it  was  slowly  rising.  This  is  a  good  rep- 
resentation of  the  manner  in  which  most  of  the  mount- 
ain chains  are  made  and  shaped. 

Take  another  ex- 
ample, represented 
in  Fig.  70.  Here  it 
is  obvious  that  the 
strata  a  were  first 
deposited  horizon- 


rig.  TO. 


tally  ;  then  the  middle  part  or  axis  of  the  mountain  was 
thrust  up,  tilting  the  strata  a,  and  after  the  tilting  was 
completed  the  strata  b  were  deposited.  In  Fig.  71  we 


Fig.  71. 


see  a  somewhat  different  state  of  things.  The  strata  a 
and  b  were  both  deposited  before  the  axis  of  the  mount- 
ain rose,  and  therefore  were  tilted  up  together.  After- 
ward the  strata  c  were  formed.  Now  if  the  strata  a 
and  b  are  the  same  in  character  in  the  two  cases,  the 
mountain  represented  by  Fig.  71  is  of  much  later  date  in 
the  world's  growth  than  that  represented  in  Fig.  70. 


CONSTRUCTION    OF    THE    EARTH.  143 

227.  Valleys- — Intimately  connected  with  the  subject 
of  the  formation  of  mountains  is  that  of  the  formation 
of  valleys.  These  are  chiefly  of  three  kinds:  1.  Valleys 
of  undulation.  These  occur  between  the  hills  and 
mountains  that  are  raised  by  flexures  of  the  earth's  stra- 
ta, as  represented  in  Fig.  52.  2.  Valleys  of  dislocation. 
These  are  caused  by  fissures  in  strata,  as  represented  by 
Fig.  55.  Where  the  strata  are  very  thick,  such  valleys 
are  colossal  in  size  and  bold  in  their  features.  3.  Val- 
leys of  denudation.  These  vary  much,  according  as  the 
rocks  acted  upon  by  the  water  are  soft  or  firm.  In  Fig. 
72  is  represented  an  example  of  valleys  formed  by  de- 


rig.  72. 

nudation.  The  strata  here  are  not  all  continuous,  but 
portions  of  some  of  them  have  been  worn  away  by  wa- 
ter, leaving  the  hills  with  valleys  between  them. 

228.  Volcanoes. — These  are  constructed  in  a  different 
way  from  common  mountains.  They  are  made  out  of 
the  matters  which  are  ejected  from  them,  so  that,  as  long 
as  a  volcano  is  active,  the  work  of  construction  is  to  some 
extent  going  on.  The  solid  matters  ejected  are  chiefly 
lava,  cinders,  and  cinders  moistened  and  forming  in  their 
solidification  what  is  called  tufa.  The  tendency  in  the 
construction  is  to  the  form  of  a  cone,  which  is  sometimes 
very  perfectly  carried  out,  as  seen  in  the  grand  volcano 
of  Japan,  Fusiyama,  the  summit  of  which  is  represented 
in  Fig.  73  (p.  144).  It  stands  14,000  feet  high.  It  has 
in  its  top  an  oval  opening,  one  diameter  of  which  is  3300 
feet,  and  another  1800  feet,  and  the  depth  is  1000  feet. 
This  volcano  has  long  been  inactive,  the  latest  eruption 
recorded  having  occurred  in  1707.  But  two  months  in 
the  year,  July  and  August,  is  the  summit  sufficiently  free 
from  snow  to  permit  the  ascent,  and  then  the  natives  are 


-  .  -^-^rr=^JL. ^-^"~ "~—-^ 


Fig.  73. 


CONSTRUCTION  OF  THE  EARTH. 


145 


very  busy  in  making  their  pilgrimages  to  the  mountain, 
which  they  consider  very  sacred,  and  call "  matchless." 
The  steepness  of  the  sides  of  volcanoes  depends  on  the 
material  of  which  they  are  formed,  being  steepest  when 
the  material  is  cinders,  and  least  so  when  it  is  lava.  Most 
frequently  volcanic  cones  are  of  a  mixed  character,  hav- 
ing layers  of  lava  and  of  consolidated  cinders  mingled  to- 
gether. This  is  represented  in  Fig.  74,  which  is  intended 


Fig.  74. 


to  be  a  section  through  some  volcanic  cones.  The  parts 
made  of  short  vertical  lines  represent  the  layers  of  lava, 
and  the  long  lines  represent  the  layers  of  ashes  and  cin- 
ders. Irregularities  occur  in  the  forms  of  volcanic  cones 
from  various  circumstances.  For  example,  a  wind  pre- 
vailing in  one  direction  may  make  ejected  cinders  accu- 
mulate on  one  side  of  a  crater  more  than  on  another. 
The  edge  of  a  crater  may  be  thrown  over,  as  in  the  case 
of  Vesuvius  (§  195).  Lava  may  burst  out  through  a  fis- 
sure, and,  solidifying,  cause  accumulation  on  one  side  of 
the  cone. 

229.  Trap  Rocks. — Though  these  rocks  have  a  decided 
resemblance  to  volcanic  rocks  in  their  composition,  the 
eminences  formed  by  them,  some  of  which  are  lofty 
enough  to  be  called  mountains,  were  constructed  in  a 
very  different  manner.  They  are  igneous,  and  yet  not 
volcanic.  They  were  thrust  up  from  below,  a  molten 
mass  pushing  up  the  superincumbent  strata  before  them, 
and  gradually  became  solid  by  cooling.  They  came  up 
through  fissures  in  rocks,  forming  dikes,  so  called,  in 
these  fissures.  If  the  trap  was  not  so  hard  as  the  rocks 

G 


146 


GEOLOGY. 


Fig.  75. 


in   which  the  fissure  was  made,  then   the   denudation 

which  followed  left  what 
is  called  a  sunk  dike,  as 
seen  in  Fig.  75.  But  if, 
as  is  usually  the  case,  the 
fissured  rocks  were  soft- 
er than  the  trap,  it  left  a 
raised  dike,  as  represented  in  Fig.  76.  Hugh  Miller,  in 

commenting  upon  the 
trap  eminences  or  dikes 
in  and  about  Edinburg, 
on  one  of  which  stands 
the  Castle  of  Edinburg, 

compares  the  work  of  the  denuding  agencies  to  the  work 
of  the  sculptor,  because,  as  he  brings  out  his  figures  in 
alto  relievo  by  chipping  away  around  them,  so  have  these 
agencies  brought  out  in  bold  relief  the  grand  trap  prom- 
inences by  scooping  away  the  soft  shales  and  sandstones 
which  flanked  them.  The  same  can  be  said  of  the  twin 
prominences,  East  and  West  Rock,  that  add  so  much  to 
the  scenery  about  New  Haven.  Sandstone  was  all  about 
them,  perhaps  even  covered  them,  until  the  sculptor,  wa- 
ter, with  its  tides,  and  waves,  and  currents,  removed  it. 
"  Trap  scenery,"  remarks  Hugh  Miller,  "  may  be  de- 
scribed generally  as  eminently  picturesque.  From  tho 
circumstance  that  its  eruptive  masses  rise  often  from 
amid  level  fields,  and  that  its  hard,  abrupt  beds,  dikes, 
and  columns  alternate  often  with  rich,  soft  strata,  that 
decompose  into  fertile  soils,  it  abounds  in  striking  con- 
trasts. The  soft  plain  ascends  often  at  one  stride  into  a 
hill  fantastically  rugged  and  abrupt,  and  bare  and  frac- 
tured precipices  overtop  terraced  slopes  or  level  plat- 
forms rich  in  verdure." 

230.  How  the  Trap  Rocks  were  Formed.— These  rocks 
were  not  formed  below  and  then  lifted  into  their  places, 
but,  as  I  have  before  stated,  the  material  in  a  molten 
state  was  thrust  up,  and  there  cooled  off  and  solidified 


CONSTRUCTION    OF   THE    EARTH. 


147 


under  the  pressure  of  rocky  strata,  which  it  had  lifted 
up,  and  which  was  covered  with  water  probably  of  con- 
siderable depth.  This  could  not  happen  without  crea- 
ting great  commotion,  especially  if  there  were  fractures  in 
the  superincumbent  strata,  letting  down  the  water  upon 
the  surface  of  the  red  molten  mass.  Hugh  Miller,  in  his 
magnificent  description  of  what  may  be  imagined  to  have 
occurred  in  the  emergence  of  the  trap  rocks,  speaks  of 
steam  and  flame  issuing  from  the  fissures  up  through  the 
boiling  waters.  This  may  all  be  correct ;  but  when  he 
speaks  also  of  the  heavens  being  dark  with  ashes,  as  if  a 
real  volcano  were  in  action,  the  facts  which  the  rocks  now 
reveal  to  us  hardly  warrant  such  imaginings.  Though  fire 
is  the  agent  in  both  cases,  the  formation  of  trap  rocks  dif- 
fers very  decidedly  from  the  building  up  of  a  volcanic  cone. 
The  open  throat  or  chimney,  through  which  materials  of 
various  kinds  are  thrown  up  from  the  volcano,  is  wanting 
when  the  trap  rocks  are  elevated  into  their  position. 

It  is  in  the  cooling  and  solidification  of  the  molten 
mass  that  the  prismatic,  pillar-like  form  is  sometimes  so 
perfectly  assumed,  as  exhibited  in  the  Giant's  Causeway, 
Fingal's  Cave,  etc.  The  igneous  origin  of  these  prisms 
fairly  entitle  them  to  the  name  of  "  furnaced  pillars," 
which  the  Ettrick  Shepherd  has  given  them. 

231.  Veins. — There  are  found  in  the  rocks  what  are 
called  veins — that  is,  fissures  filled  with  rocky  material, 

or  with  metallic  ores,  or  with 
both.  When  they  are  filled 
with  rocky  material,  this  is 
sometimes  the  same  with  the 
rock  itself  in  which  the  veins 
are,  and  sometimes  it  is  of  a 
different  composition.  Some- 
times one  vein  traverses  an- 
other, as  is  shown  in  Fig. 
77.  This  is  often  the  case 
Fig.  77.  with  veins  of  granite.  Such 


GEOLOGY. 


veins  have  often  penetrated  through  the  overlying  depos- 
its, and  flowed  over  the  rocks  which  they  have  displaced, 
as  shown  in  Fig.  78.  Sometimes  one  vein  is  displaced 
or  faulted  by  another,  as  repre- 
sented in  Fig.  79.  Here  is  an 


Fig.  78. 

outline  of  the  section  of  a  boulder  found  by  Prof.  Hitch- 
cock in  West  Hampton,  Mass.  It  is  a  fragment  of  a 
granite  rock  which  was  traversed  by  three  granitic  veins. 
These,  as  seen  in  the  boulder,  are  bed,  ef,  and  gh.  The 
vein  bed  was  made  first.  The  other  two  were  made 
afterward,  displacing  or  faulting  the  first,  as  you  see  in 
the  figure.  As  the  three  veins  were  made  at  three  dif- 
ferent times,  they  are  three  different  varieties  of  granite. 
Here,  then,  is  a  record  of  four  different  formations  of 
granite,  the  rock  itself  and  the  three  veins,  and  how  long 
the  intervals  were  between  them  we  know  not — they 
may  have  been  ages. 

Veins  differ  from  dikes  in  various  respects.  They  are 
apt  to  be  irregular  in  shape,  larger  at  one  point  than  at 
another,  while  dikes  are  regular  and  uniform.  Veins 
are  often  compound,  containing  a  variety  of  materials, 
sometimes  a  considerable  variety,  while  dikes  are  sim- 
ple, containing  only  one  kind  of  material,  as  some  volcan- 
ic mineral  or  trap.  And  when  a  vein  has  only  one  kind 
of  material,  this  never  has  the  arrangement  that  a  dike 
often  presents — viz.,  a  columnar,  arrangement,  as  if  one 
block  were  placed  above  another  from  the  bottom  to  the 
top  of  the  dike.  Those  veins  which  are  compound  have 
a  very  different  arrangement  from  the  columnar  one  of 


THE    EARTH.  149 


the  dikes.  It  is  a  banded  arrangement — that  is,  the  ma- 
terials are  in  bands  parallel  with  the  walls  of  the  vein. 
The  bands  may  be  few  in  number  or  numerous.  If  there 
be  metallic  ore  in  a  banded  vein  the  rocky  material  is 
called  the  vein-stone  or  gangue. 

Dikes  are  due  to  the  injection  upward  of  melted  ma- 
terial into  openings  or  fissures  in  the  rocks ;  but  the  man- 
ner in  which  veins  have  been  produced  is  by  no  means  as 
yet  fully  understood,  and  there  have  been  much  discus- 
sion and  speculation  about  it. 

The  distinctions  between  dikes  and  veins  are  generally 
recognized  among  geologists  as  I  have  pointed  them  out, 
but  sometimes  there  is  a  little  confusion  in  the  use  of 
these  terms.  The  term  lode  is  often  given  to  veins,  but 
seldom  to  any  except  those  which  are  metallic. 

232.  Drift — This  term  is  applied  to  fragments  of  rocks 
which  have  been  scattered  over  some  portions  of  the 
earth's  surface  by  other  means  than  the  flowing  of  water. 
The  fragments  vary  in  size  from  grains  up  to  those  which 
are  many  tons  in  weight.  When  they  are  of  any  consid- 
erable size  they  are  called  boulders.  They  are  supposed 
to  have  been  scattered  by  means  of  icebergs  or  glaciers, 
or  both.  Drift  is  not  found  at  all  in  tropical  climates. 
In  North  America  it  appears  in  Canada,  New  England, 
the  State  of  New  York,  and  in  all  the  states  west  of  that 
region  in  the  same  latitude.  In  Europe  also  it  is  con- 
fined to  the  northern  part.  From  comparison  of  the 
drift  with  the  stationary  rocks,  and  from  other  observa- 
tions, it  is  manifest  that  all  the  drift  came  from  the  north. 
In  the  southern  hemisphere,  however,  it  came  from  the 
opposite  direction.  In  both  cases  its  movement  was  from 
the  pole  toward  the  equator.  The  distance  to  which 
boulders  have  been  carried  is  sometimes  very  great,  even 
hundreds  of  miles.  We  know  where  they  came  from  by 
their  composition  and  other  circumstances.  Sometimes 
long  trains  of  boulders  are  traced,  as  if  an  iceberg  slowly 
sailed  along,  dropping  continually  as  it  went  its  rocky 


150  GEOLOGY. 

freights.  In  such  cases  it  is  very  easy  to  find  the  source 
of  the  boulders.  Drift,  in  its  passage,  left  in  many  places 
its  marks,  as  scratches,  and  furrows,  and  smoothings. 
Sides  of  mountains  exhibit  often  these  marks,  and  so 
high  up  in  this  country  that  we  know  that  there  is  only 
one  mountain  in  New  England,  Mount  Washington,  that 
lifted  its  head  above  this  drift  action.  I  will  not  dwell 
longer  on  this  interesting  subject  here,  as  it  will  be 
brought  before  you  more  particularly  in  another  part  of 
this  book. 

233.  Subsidences  and  Elevations  of  the  Earth's  Crust. 
— You  will  find,  as  I  proceed  to  notice  the  different  ages 
of  the  earth's  formation,  that  different  portions  of  its 
crust  were  alternately  submerged  under  the  waters  and 
elevated  above  them.  This  was  not  done  by  any  sud- 
den convulsive  movements, but  slowly,  perhaps  as  slowly 
as  the  change  of  level  now  occurring  in  Sweden  and 
some  other  countries,  as  noticed  in  §  206.  These  altern- 
ate subsidences  and  elevations,  which  were  generally 
several,  sometimes  many  in  number,  were  necessary,  as 
you  will  see,  for  the  formation  and  arrangement  of  the 
various  strata  that  make  up  the  earth's  crust.  Some- 
times subsidences  have  been  prolonged  through  even 
many  ages.  Lyell  speaks  of  one  over  a  large  area  in 
England  and  Wales  which  continued  so  long  that  strata 
over  six  miles  (32,000  feet)  in  thickness  were  deposited 
during  the  time.  In  all  this  period,  covering  not  an  age 
merely,  but  successive  ages,  there  was  an  ocean's  bed  in 
that  region,  and  this  bed  sank  gradually  and  quietly  as 
the  deposits  of  solid  matter  were  made  upon  it  from  the 
water  lying  above  it.  In  no  one  of  the  ages  of  the 
earth's  formation  was  there  so  remarkable  an  alterna- 
tion of  subsidences  and  elevations  as  in  that  one  in  which 
the  coal  was  made  and  laid  down.  Each  bed  of  coal,  as 
you  will  learn  more  fully  in  another  chapter,  was  made 
from  vegetation  grown  upon  the  surface,  and  this  being 
submerged  by  a  subsidence,  rock  was  formed  over  it. 


CONSTEUCTION    OF  THE   EARTH.  151 

Then,  to  make  another  bed  of  coal,  there  was  an  eleva- 
tion for  another  growth,  which  was  in  its  turn  sub- 
merged, to  be  covered  by  a  rocky  deposit.  Where  there 
are  many  beds  of  coal  there  must  have  been  many  of 
these  alternate  movements. 

234.  Pebbles,  Sand,  and  Earth. — In   several  different 
connections  I  have  remarked  upon  the  ways  in  which 
the  rocks  are  worked  up  into  pebbles,  sand,  and  earth. 
You  have  seen  that,  while  other  agencies  are  at  work, 
water,  either  directly  or  indirectly,  is  the  grand  agent 
— directly  by  its  own  erosive  power,  and  indirectly  by 
grinding  fragments  of  rock,  from  the  large  to  the  mi- 
nute, against  each  other.     By  these  means  chiefly  has 
the  soil  all  been  prepared  ;  and  it  is  nothing  but  commi- 
nuted rock,  with  soluble  matter  from  some  of  the  rocks 
dissolved  in  the  water  diffused  through  it.     It  is  true 
that  when  seeds  are  put  into  the  soil  thus  prepared  ad- 
ditions are  made  to  it  from  the  decay  of  vegetable  mat- 
ter, but  this  is  a  mere  return  of  such  matter  to  the  min- 
eral condition.     All  was  originally  mineral — earth,  wa- 
ter, and  air ;  and  in  plants  and  animals  we  have  life  act- 
ing only  upon  mineral  matter,  giving  it,  for  the  time  be- 
ing, new  properties.     It  is  a  very  important  item  in  the 
construction  of  the  earth  for  man  that  the  soil  should  be 
thus  prepared,  by  what  may,  in  one  sense,  be  considered 
a  destructive  process,  but  in  another  the  putting  the 
material  of  wThich  the  rocks  are  composed  into  a  special 
form  for  a  special  purpose.     If  this  were  not  done,  vege- 
tation and  animal  life  could  have  flourished,  at  best,  to 
but  a  scanty  extent. 

235.  Earth-worms  and  Ants. — These  animals,  apparent- 
ly so  insignificant,  are  real  geological  workers,  accom- 
plishing in  the  aggregate  great  results  in  preparing  the 
soil  to  produce  food  for  man   and  beast.      The  earth- 
worm burrows  in  the  earth,  loosening  it,  and  leaving  his 
casts  here  and  there.     He  is  not  confined  to  loose  soils, 
but  is  ever  encroaching  upon  hard  spots,  especially  if 


152  GEOLOGY. 

they  be  wet,  as  any  gardener  may  see  occasionally  in 
the  trodden  walks.  He  does  more  than  loosen  the  soil. 
He  brings  it  up  in  a  comminuted  state,  as  the  casts  will 
show,  leaving  his  burrows  below  to  cave  in  by  the 
weight  of  the  earth  above  them.  Some  observations 
have  been  made  which  show  that  these  operations  are 
of  great  extent  and  importance.  Mr.  C.  Darwin,  who 
made  many  such  observations,  says  that  "although  the 
notion  may  appear  at  first  startling,  it  will  be  difficult  to 
deny  the  probability  that  every  particle  of  earth  form- 
ing the  bed  from  which  the  turf  in  old  pasture-land 
springs  has  passed  through  the  intestines  of  worms." 
If  you  look  among  the  spires  of  grass  you  will  find  the 
casts  of  these  worms  scattered  about,  for  they  are  al- 
ways at  work  swallowing  earth  and  disgorging  it,  either 
upon  the  surface  or  into  their  burrows.  The  tendency 
of  water  is  to  wash  from  the  surface  the  finer  portions 
of  the  soil,  carrying  it  away  or  down  into  the  ground, 
thus  leaving  the  coarser  parts  on  the  surface ;  but  the 
earth-worms  can  remedy  this  difficulty  by  bringing  up 
the  comminuted  matter.  Furnishing  bait,  then,  for  fish- 
ing is  but  a  small  part  of  the  earth-worm's  vocation. 

The  ants  are  also  at  work  somewhat  in  the  same  way, 
choosing  drier  spots  than  the  earth-worms  do.  You 
see  them  in  multitudes  on  the  dry  garden  walk,  where 
they  make  their  galleries  underneath,  from  which  they 
bring  the  materials  for  their  little  piles  on  the  surface. 
They,  by  loosening  the  soil,  help  to  produce  the  vegeta- 
tion which  you  are  continually  at  work  to  destroy ;  but, 
though  operating  against  you  in  the  walk,  they  are  every 
where  else  doing  a  good  work  for  you  in  your  garden. 
They  are  especially  useful  in  tropical  climates,  where 
they  rapidly  take  to  pieces,  as  we  may  say,  the  accumu- 
lations of  dead  vegetable  substance,  and  mingle  it  with 
the  soil.  Dr.  Livingstone,  the  great  traveler,  says  of  the 
labors  of  the  ants  in  the  forests  of  Africa,  "These  insects 
are  the  chief  agents  employed  in  forming  a  fertile  soil. 


CONSTRUCTION    OF   THE   EARTH.  153 

But  for  their  labors,  the  tropical  forests,  bad  as  they 
are  now  with  fallen  trees,  would  be  a  thousand  times 
worse."* 

236.  Corals. — Coral  animals,  which  are  of  the  class 
called  Polypes,  are  the  most  important  organic  or  living 
agencies  that  have  contributed  to  the  construction  of 
the  earth.  These  animals  are  very  small,  most  of  them 
exceedingly  so,  being  less  than  the  size  of  a  pin's  head. 
They  live  in  companies  together,  sometimes  each  a  sep- 
arate animal,  and  sometimes  united  together  by  a  fleshy 
mass,  making  what  is  called  a  polypidom,  or  household 
of  polypes.  When  separate,  each  sits  like  a  cap  on  the 
summit  of  a  column  of  carbonate  of  lime,  and  there  takes 
in  its  food  as  it  can  catch  it  from  the  passing  water.  To 
this  mineral  column  he  is  continually  adding,  and  the 
process  is  a  singular  one.  The  animal  is  ever  dying  be- 
low and  growing  above ;  and  as  the  column  may  be  con- 
sidered his  skeleton,  he  may  be  said  to  be  continually 
leaving  dead  skeleton  below  him  as  he  grows.  The 
process  is  essentially  the  same,  though  modified,  in  the 
case  of  the  polypidom.  In  this  work  each  animal  does 
but  little,  but  in  the  aggregate  vast  results  are  accom- 
plished. In  the  ages  that  are  past  these  little  animals 
have  made  immense  additions  to  the  limestone  in  the 
earth's  crust,  and  they  are  continuing  their  work  now. 
The  rocks  which  result  from  their  work  are  not  really 
built  up  by  these  animals.  They  furnish  the  material, 
which  is  broken  up  and  changed  into  limestone,  though 
there  are  imbedded  in  many  of  these  rocks  the  coral 
forms.  And  the  material  is  not  furnished  by  these  ani- 
mals alone,  for  shell-fish  and  other  animals  abound  wher- 
ever there  are  corals,  and  their  remains  add  to  the  mate- 

*  I  have  noticed  the  earth-worms  and  ants  in  this  chapter,  rather 
than  in  the  chapter  on  present  changes,  partly  because  they  have  un- 
doubtedly been  great  geological  workers  in  past  ages,  and  partly  be- 
cause it  is  appropriate  to  consider  their  work  in  connection  with  the 
general  view  of  the  preparation  of  the  soil  for  the  use  of  man, 

G2 


154  GEOLOGY. 

rial  of  the  rocks.     Especially  is  this  the  case  with  the 
shells. 

237.  Coral  Reefs. — Along  many  shores  there  are  ridges 
or  reefs  made  by  coral  animals.  The  mode  of  their  con- 
struction I  will  describe.  These  animals  do  not  begin 
their  work  on  the  edge  of  the  land,  for  they  like  clear 
water,  which  can  not  be  had  close  to  the  shore.  But 
there  is  a  limit  away  from  the  land  beyond  which  they 
will  not  work,  and  this  limit  depends  on  the  depth  of 
water.  They  can  not  live  beyond  a  depth  of  about  100 
feet,  and  most  often  they  choose  a  depth  of  20  or  30  feet 
to  begin  their  operations.  Where  the  water  deepens  rap- 
idly from  the  shore,  they  are  not  as  far  away  from  it  as 
where  it  deepens  gradually.  Coral  animals  are  confined 
to  certain  climates.  Almost  'all  the  shelving  shores  in 
tropical  seas  are  lined  by  the  reefs  which  they  make. 
There  is  a  remarkable  exception  in  the  case  of  the  west- 
ern coast  of  South  America.  Here  there  are  no  corals, 
while  they  abound  on  the  eastern  coast  in  the  same  lati- 
tudes. The  reason  is  that  the  western  coast  has  sweep- 
ing along  it  a  cold  current  from  the  antarctic  regions. 
Many  of  the  coral  reefs  are  not  yet  raised  up  to  the  sur- 
face, and  these  hidden  reefs  are  very  dangerous  to  nav- 
igation. Some  reefs  are  of  very  great  extent.  Along 
the  coast  of  New  Holland  there  is  one  over  1000  miles 
in  length,  and  for  350  miles  in  one  part  of  it  there  is  no 
passage  through  it.  Reefs  are  spoken  of  as  being  of  two 
kinds,  fringing  and  barrier ;  the  former  being  near  the 
shore,  and  the  latter  at  some  distance  from  it,  with  a  deep 
channel  between.  The  fringing  reefs  are  very  apt,  after 
a  time,  to  become  a  part  of  the  main  land.  The  reason 
is  that  there  is  a  continual  washing  of  material  into  the 
space  between  the  land  and  the  reef,  both  from  the  land 
and  the  sea,  chiefly  the  former.  Indeed,  Florida  was  all 
made  in  this  way,  reefs  having  continually  formed  age 
after  age,  and  then  joined  to  the  main  land.  Many  isl- 
ands have  been  formed  by  coral  animals.  A  large  part 


CONSTRUCTION    OF    THE    EARTH. 


155 


of  the  islands  of  the  Polynesian  Archipelago,  as  well  as 
many  of  those  of  the  Indian  Ocean,  came  from  this  source. 
238.  Atolls. — This  name  is  given  to  certain  coral  isl- 
ands having  a  peculiar  arrangement,  one  of  which,  Whit- 
sunday Isle,  is  represented  in  Fig.  80.  There  is,  as  you 


rig.  so. 

see,  a  strip  of  land  inclosing  a  lake  called  a  lagoon.  In 
some  atolls  this  strip  of  land  is  unbroken,  while  others 
have  one  or  more  openings,  so  that  the  lagoon  forms  a 
harbor.  These  atolls  are  of  various  shape,  sometimes 
almost  circular,  sometimes  long  and  narrow,  having  va- 
rious bends  and  indentations  in  the  margin  of  land. 
Their  size  varies  from  half  a  mile  up  to  sixty  miles 
across.  The  manner  in  which  they  are  constructed  can 
be  explained  by  Figs.  81  and  82.  We  will  suppose  an 


Fig.  81. 


island  around  which  the  coral  animals  build  reefs ;  a  a, 
Fig.  81,  being  the  reefs,  and  b  b  the  water  between  then 
and  the  island.  But  in  the  figure  a  mere  point  in  the 
middle  of  the  island  is  seen  standing  out  of  the  water, 
although  the  bottom  of  the  reefs  is  far  below  the  lowest 


156  GEOLOGY. 

depth  which  coral  animals  reach.  What  is  the  explana- 
tion? It  is  supposed  to  be  this.  When  these  animals 
just  began  to  make  the  reefs,  the  island  stood  far  up  out 
of  the  water ;  but  as  fast  as  the  reefs  were  built  up  the 
island  subsided,  keeping  the  surface  of  the  reefs  all  the 
time  of  the  subsidence  under  the  water.  The  rate  of 
subsidence  must  have  been  very  slow  to  correspond  with 
the  slow  growth  upward  of  the  corals,  which  has  been 
calculated  to  be  only  the  one  eighth  of  an  inch  in  a  year. 
In  a  completed  atoll,  the  island  having  wholly  disap- 
peared, we  have  a  state  of  things  indicated  in  Fig.  82, 

_ a  a  a  representing  a 

It^  section  of  the  mar- 


Fig-  82-  gin  of  land,  and  b  b 

the  lagoon.  An  atoll,  then,  may  be  looked  upon  as  uthe 
tomb  and  monument  of  an  island  altogether  buried  be- 
neath the  waves." 

There  are  groups  of  these  singular  islands,  in  some 
cases  extending  over  large  spaces.  In  the  Pacific  Ocean 
there  is  a  band  of  such  groups  4500  miles  long,  and  va- 
rying from  200  to  600  miles  in  breadth. 

Many  atolls  rise  up  from  a  depth  of  2000  feet,  and 
therefore  are  mountains  of  coral  rock  standing  in  the 
water  over  a  third  of  a  mile  in  height.  At  the  rate  of 
an  eighth  of  an  inch  a  year,  it  took  the  coral  animals 
192,000  years  to  build  such  mountains. 

239.  Calcareous  Shells. — I  have  said  that  in  the  for- 
mation of  the  coral  rocks  there  were  contributions  of 
shells.  In  fact,  they  every  where  contribute  material 
for  the  limestones ;  but  in  this  case,  as  well  as  in  others, 
the  great  work  of  furnishing  material  is  done  by  very 
small,  even  minute  animals.  The  shells  of  such  animals 
have  formed  extensive  strata  in  various  parts  of  the 
earth's  crust.  In  Fig.  83  you  see  represented  the  shells 
of  some  of  the  foraminifera,  a  class  of  these  minute  ani- 
mals, so  named  because  their  chambers  communicate  by 
numerous  foramens  or  pores.  The  microscopic  animals 


CONSTRUCTION    OF    THE    EARTH.  157 

that  inhabit  these 
many  -  chambered 
shells  are  com- 
posed of  a  gelat- 
inous fleshy  sub- 
stance, and  have 
minute  prolonga- 
tions which  they 
Fig- 83>  can  throw  out  and 

retract,  and  which  they  use  for  swimming,  crawling,  and 
gathering  their  food.  There  is  great  variety  in  the 
shells  of  the  different  species,  and  the  regularity,  beauty, 
and  delicacy  of  structure  of  these  shells  are  very  won- 
derful. In  view  of  the  vast  amount  of  rocky  material 
which  such  minute  animals  have  added  in  past  ages,  and 
are  now  adding,  to  the  earth's  crust,  it  may  well  be  said 
that  the  additions  made  by  the  remains  of  the  larger  an- 
imals, such  as  elephants,  lions,  crocodiles,  whales,  etc., 
are  utterly  insignificant  in  the  comparison.  There  is  one 
division  of  the  foraminifera  that  ..are  not  microscopic, 
viz.,  the  nummulites,  one  of  which  you  see  at  b.  They 
are  of  various  sizes,  from  very  minute  up  to  the  size  of 
an  inch  and  a  half  in  diameter.  The  name  comes  from 
the  Latin  word  nummus,  money,  because  the  shell  re- 
sembles a  coin  in  shape.  Sometimes  limestone  is  com- 
posed entirely,  or  nearly  so,  of  nummulites,  and  then  is 
called  nummulitic  limestone.  The  Sphinx  and  the  Pyr- 
amids are  made  of  this  rock.  It  constitutes  the  princi- 
pal part  of  several  mountain  ranges  in  the  south  of  Eu- 
rope, as  the  Alps  and  Pyrenees. 

In  soundings  in  different  parts  of  the  Atlantic  Ocean, 
between  Ireland  and  Newfoundland,  as  far  south  as  the 
Azores,  there  has  been  brought  up  a  soft,  sticky  mud, 
which  has  been  called  oaze.  This,  on  being  dried  and 
examined  with  the  microscope,  was  found  to  consist  of 
the  minute  shells  of  foraminifera.  As  these  shells  are 
composed  of  carbonate  of  lime,  when  an  acid,  as  the  sul- 


158  GEOLOGY. 

phuric,  is  added  to  oaze,  brisk  effervescence  occurs,  be- 
cause the  acid,  taking  the  lime,  sets  the  carbonic  acid 
gas  free.  Here  there  is  an  immense  chalk  deposit  going 
on  over  a  large  area ;  and  in  such  lengths  of  time  as  were 
occupied  by  deposits  and  solidifications  in  ages  gone  by, 
this  deposit  may  become  hundreds  of  feet  thick,  and  be 
solidified  into  rock.  In  limestone  strata  quarried  near 
Paris  the  rock  is  composed  to  a  large  extent  of  shells 
no  larger  than  millet-seeds.  Ehrenberg  has  discovered 
in  that  form  of  limestone  which  we  call  chalk,  animals 
much  smaller  than  this — so  small  that,  where  they  nearly 
constitute  the  whole  mass,  as  they  do  in  the  chalk  of 
southern  Europe,  there  are  over  a  million  of  them  in  ev- 
ery cubic  inch.  Soldani  collected  from  less  than  an 
ounce  and  a  half  of  rock  from  the  hills  of  Casciana,  in 
Tuscany,  10,454  shells  of  foraminifera  of  various  species. 
Some  of  the  species  are  so  minute  that  it  would  require 
over  a  thousand  of  the  shells  to  weigh  a  grain. 

240.  Silicious  Shells. — You  have  already  learned  in 
§  116  that  silica,  or  flint,  is  dissolved  by  certain  means  in 
water,  and  then  is  gathered  up  by  plants  and  animals, 
becoming  again  solid  in  soluble  silica.  There  are  very 
extensively  scattered  in  the  earth  innumerable  minute 
animals  and  vegetables  which  thus  gather  this  material 
from  the  water  in  which  they  live,  and  then,  as  they 
die,  their  silicious  shields  or  shells  are  deposited,  and 
much  of  the  deposit  becomes  in  time  solid  rock.  These 
shields  present  great  variety  of  figure,  and  are  very  beau- 
tiful as  seen  under  the  microscope.  In  Fig.  84  you  see 

represented  three 
of  the  forms  of 
shells  of  this  kind, 
of  which  a  stratum 

Actinocyclus.  Coscinodiscus   of  wnite  clay  about 

patina.  •> 

Fig.  84.  Richmond,  Va.,  is 

chiefly  composed.  The  stratum  is  from  twelve  to  thir- 
ty feet  thick,  and  is  of  great  extent.  The  tripoli,  or  rot- 


CONSTRUCTION  OF  THE  EAKTH.          159 

ten-stone  of  Germany,  forming  beds  sometimes  fourteen 
feet  thick,  is  made  up  mostly  of  silicious  shells  so  mi- 
nute that  a  cubic  inch  contains  forty-one  thousand  million 
(.41,000,000,000),  the  weight  of  a  single  shell  being  cal- 
culated to  weigh  the  y^  millionth  part  of  a  grain.  Si- 
licious deposits  from  vegetables  and  animals  are  often 
mingled  with  calcareous  deposits,  and  hence  came'  for  the 
most  part  the  flint-stones,  which,  as  you  will  see  here- 
after, are  so  often  found  in  chalk.  One  tenth  of  the  oaze 
(§  239)  is  silicious.  So  much  agency  are  the  minute 
silicious  animalcules  and  plants  known  to  have  had  in 
furnishing  material  for  silicious  rocks,  that  some  have 
supposed  that  most  rocks  of  this  kind  have  received  their 
material  from  this  source. 

I  remark  in  passing  that,  although  the  diatoms  of 
which  some  forms  are  given  in  Fig.  84  have  heretofore 
always  been  considered  as  animalculse,  Professor  Dana 
states  that  they  are  now  regarded  as  vegetable. 

241.  Seas,  Lakes,  and  Rivers. — I  have  thus  shown  you 
what  means  have  been  employed  in  the  building  up  of 
that-  part  of  the  earth  which  is  included  under  the  gen- 
eral term  land.     The  great  cavities  of  the  sea,  "  the 
store-houses"  in  which  God  "layeth  up  the  depth,"  we 
know  less  about,  and  our  researches  are  confined  mostly 
to  the  comparatively  shallow  portions  of  the  ocean  which 
skirt  the  land.     The  manner  in  which  the  rivers  that 
run  into  the  sea  are  made  I  need  not  stop  to  point  out 
to  you.      The  streamlets  made  by  every  shower  illus- 
trate that  subject,  so  that,  with  what  has  already  been 
said  in  regard  to  rivers,  your  own  observation  can  give 
you  a  proper  insight  into  it.     The  same  can  be  said,  for 
the  most  part,  of  the  lakes. 

242.  Plan  in  the  Construction  of  the  Earth. — Enough 
has  been  developed  in  what  I  have  said  of  the  construc- 
tion of  the  earth  to  show  you  that,  although  there  have 
been  commotion  and  much  apparent  confusion,  there  has 
been  a  well-ordered   plan  throughout  all  the  changes, 


160  GEOLOGY. 

aiming  at  the  eventual  fitness  of  the  earth  for  man  as  his 
habitation.  This  will  be  much  more  obvious  to  you  as 
we  proceed  to  notice  the  different  ages  of.  the  earth's 
preparation,  and  show  how  the  continents  have  grown 
to  be  what  they  are  by  successive  additions.  In  the 
case  of  each  continent,  the  form  of  the  land  first  lifted 
above  the  surface  of  the  waters  had  a  manifest  reference 
to  that  form  which  was  to  be  given  to  it  when  it  was  to 
be  completed  and  made  fit  for  the  use  of  man.  There 
was  in  the  beginning  a  germ,  and  the  gradual  unfolding 
of  it  has  been  beautifully  traced  out  by  the  labors  of  the 
geologist. 


CHAPTER  XII. 

RECORD    OF   LIFE   IN   THE   ROCKS. 

243.  Life  in  the  Different  Ages  of  the  Earth. — There 
was  a  period,  and  that  a  very  long  one,  as  you  will  see 
in  the  next  chapter,  in  which  there  was  no  life  upon  the 
earth.  But  after  that  period  was  passed,  life,  vegetable 
and  animal,  was  introduced,  and  became,  as  you  have  al- 
ready seen,  a  great  agency  in  the  construction  of  the 
earth's  crust.  What  the  forms  of  life  were  in  the  succes- 
sion of  ages  previous  to  the  age  of  man  have  been  made 
out  by  the  geologist,  by  observing  the  remains  of  vege- 
tables and  animals  found  in  the  strata  of  the  rocks.  The 
life  of  the  world,  then,  may  be  said  to  have  written  its 
own  history  on  tables  of  stone,  and  we  are  able  to  read 
on  these  tables  the  various  changes  which  the  forms  and 
modes  of  life  have  taken  on  during  the  ages  of  the  past. 
The  lengths  of  these  successive  ages  we  can  not  make 
out  with  any  accuracy ;  we  can  not  measure  time  in  the 
far  past  of  our  earth  by  years  and  centuries  as  we  can 
in  the  present  ag& ;  but  we  can,  by  the  life-record,  learn 
the  order  of  succession,  which  has  marked  both  the  con- 
struction of  different  parts  of  the  earth  and  the  furnish- 


RECORD    OF    LIFE   IN   THE   ROCKS.  161 

ing  of  it  with  the  forms  of  life.  In  the  successive  ages 
there  have  been  variations  in  the  vegetables  and  ani- 
mals, especially  the  latter,  which  designate  these  ages, 
as  we  learn  by  reading  the  record  of  the  rocks.  The 
farther  we  go  back  in  this  record  the  less  is  the  resem- 
blance of  the  forms  of  life  in  the  past  to  those  of  the 
present,  and  the  gradual  increase  of  this  resemblance,  as 
we  come  down  from  the  first  dawning  of  life  on  the  earth 
to  the  present  age,  is  very  obvious.  This  great  fact  will 
be  developed  to  you  in  various  ways  as  we  proceed. 

244.  Nature  of  the  Evidence. — You  have  already  had 
some  glimpses  of  the  record,  and  see  what  is  the  nature 
of  the  evidence  that  it  affords.     You  have  seen  that  the 
strata  were  formed  one  upon  another  in  a  certain  order, 
and  that,  as  the  material  of  which  they  are  composed  was 
deposited,  various  remains  of  vegetables  and  animals  be- 
came mingled  with  it,  and  in  the  solidification  made  a 
part  of  the  rock.     You  see,  then,  how,  in  the  midst  of 
the  various  disturbances  of  the  strata,  the  geologist  can 
determine  the  relative  ages  of  rocks  by  examining  the 
remains  of  organic  substances  contained  in  them.     The 
strata  may  be  vertical,  or  may  even  be  so  far  bent  over 
that  the  older  rock  may  lie  upon  the  more  recent,  but 
the  life-record  reveals  the  truth ;  and,  farther  than  this, 
the  record  is  essentially  the  same  in  different  regions  of 
the  earth,  so  that  the  conclusions  of  geologists  in  one  re- 
gion may  be  applied  in  another.     For  example,  coal  is 
found  in  different  countries  in  connection  with  strata 
that  contain  certain  organic  remains ;  for,  in  the  construc- 
tion of  the  earth,  there  were  certain  periods  for  the  for- 
mation of  coal,  and  one  especial  period  for  this  purpose. 
In  whatever  country,  then,  such  strata  are  found,  it  may 
be  rationally  expected  that  coal  may  be  found  in  connec- 
tion with  them.     Other  examples  might  be  given  of  a 
similar  character,  but  this  will  suffice. 

245.  Fossils. — Any  remains  of  any  kind,  of  vegetables 
or  animals,  found  in  rocks  or  in  loose  earth,  are  called 


162  GEOLOGY. 

fossils.  The  term  comes  from  the  Latin  word  which 
means  to  dig.  The  remains  are  generally  more  or  less 
defective,  the  softer  parts  being  removed,  and  only  por- 
tions of  those  which  are  hard  being  preserved,  although 
in  some  cases  there  has  been  entire  preservation,  as 'in 
the  case  of  ancient  mammoths  found  imbedded  in  frozen 
earth  in  Siberia.  Sometimes  a  fossil  is  a  mere  trace,  as 
of  a  leaf,  or  simply  a  track  of  an  animal.  Sometimes  in 
the  fossil  there  is  not  a  particle  of  the  original  organized 
substance,  as  when  perfect  petrifaction  takes  place  (§118). 
The  mineral  substance  in  these  petrified  fossils  diifers  in 
different  cases.  The  most  common  substances  are  silica, 
carbonate  of  lime,  and  clay.  Analogous  to  petrifaction 
is  the  substitution  of  some  mineral  substance  for  the 
whole  of  an  organic  body,  as  a  shell,  the  new  substance 
making  merely  a  cast  of  it.  This  differs  from  a  petrifac- 
tion in  that  there  is  no  trace  of  the  texture  of  the  shell 
in  the  cast.  Coal,  strictly  speaking,  is  a  fossil,  for  it  is 
the  remains  of  the  vegetable  substances  from  which  it 
came,  their  texture  being  retained  in  it  more  or  less,  as 
shown  in  §  41. 

There  is  much  difference  between  different  organized 
substances  in  regard  to  their  preservation  as  fossils. 
Bones  are  very  durable,  but  the  bones  of  birds  are  sel- 
dom found,  because  they  were  borne  up  by  their  feath- 
ers as  they  decayed,  and  the  bones,  being  hollow,  were 
easily  broken.  Their  tracks,  however,  have  been  exten- 
sively observed  in  the  layers  of  rock,  as  you  will  see  far- 
ther on,  and  the  investigation  of  these,  especially  in  this 
country,  by  Hitchcock  and  others,  has  furnished  one  of 
the  most  interesting  chapters  in  geology.  Insects,  too, 
are  seldom  found,  because  they  are  so  light,  and  decay 
so  rapidly  from  the  presence  of  air  in  the  air  tubes  that 
pervade  their  bodies.  Such  hard  substances  as  shells 
are  more  largely  preserved  than  any  other  substances. 

246.  Abundance  of  Fossils. — Although  many  organ- 
ized substances,  from  the  softness  of  their  structure, 


RECORD    OF    LIFE    IX   THE    ROCKS.  163 

could  not  be  preserved  at  all,  arid  the  hard  structures  were 
liable  to  be  broken  up  or  even  destroyed,  yet  the  rocks 
abound  in  fossils.  It  is  stated  by  Agassiz  and  Gould 
that  in  most  formations  the  number  of  species  of  animals 
and  plants  found  in  any  locality  is  not  below  that  of  the 
species  now  living,  in  an  area  of  equal  extent  and  of  a 
similar  character.  For  example,  a  coarse  limestone  in 
the  neighborhood  of  Paris  contains  not  less  than  1200 
species  of  shells,  more  than  twice  the  living  species  now 
found  in  the  Mediterranean.  So,  too,  in  a  certain  kind 
of  limestone  in  New  York,  called  the  Trenton  limestone, 
there  have  been  found  170  species  of  shells,  nearly  as 
many  as  are  now  found  on  the  coast  of  Massachusetts. 
The  same  is  true  of  the  individual  plants  and  animals  as 
of  their  species.  Extensive  strata,  as  you  have  already 
seen,  are  formed  of  the  remains  of  animals,  as  corals  and 
shells,  and  the  immense  stores  of  coal  are  made  up  of  the 
remains  of  plants.  Then  there  are  the  immense  quanti- 
ties of  silicious  fossils,  for  so  they  may  be  called,  fur- 
nished chiefly  by  those  minute  plants  called  diatoms,  no- 
ticed in  §  240.  Of  these  the  microscope  shows  us  that 
there  is  a  great  variety  of  species. 

247.  Mode  of  Investigating  Fossils. — It  is  on  the  prin- 
ciples of  the  science  of  comparative  anatomy  that  the 
fossils  are  investigated.  This  science  may  be  said  al- 
most to  have  be,en  founded  by  Cuvier,  who  acquired  a 
marvelous  skill  in  prosecuting  its  researches.  From  a 
few  bones,  sometimes  even  one  small  bone,  of  an  un- 
known animal,  he  could  make  out  the  construction  of 
the  whole  frame,  and  the  character  and  habits  of  the  an- 
imal. The  principles  upon  which  this  is  done  are  very 
simple.  As  in  a  machine  each  part  has  a  relation  to  ev- 
ery other  part,  so  it  is  in  the  machinery  of  an  animal ; 
the  relations  in  this  case,  however,  being  more  perfect, 
because  the  builder  of  the  machine  has  perfect  wisdom. 
For  example,  teeth  of  a  certain  kind  not  only  require  a 
certain  kind  of  jaw,  but  a  certain  kind  of  feet  also.  An 


164  GEOLOGY. 

animal  having  the  sharp,  tearing  teeth  of  a  beast  of  prey 
would  starve  if  he  had  such  feet  as  grass-eating  animals 
have.  These  principles  almost  every  one  applies,  to  a 
certain  extent,  with  great  ease.  The  sight  of  a  tooth,  or 
claw,  or  beak  will  suggest  at  once  to  our  minds  the  hab- 
its and  the  shape  of  the  animal  to  which  it  belongs.  And 
by  careful  observation  one  can  acquire  great  skill  in  ap- 
plying these  principles  to  the  minute  parts  of  animal 
frame-work,  so  that  a  familiar  acquaintance  can  be  formed 
with  the  relations  of  each  individual  bone.  The  same 
thing  is  true,  to  a  certain  extent,  of  vegetables.  Now 
as  in  fossils  there  are  often  only  parts  of  a  vegetable  or 
animal,  this  skill  of  which  I  have  spoken  is  brought  into 
requisition,  and  by  it  the  living  beings  of  the  past  are 
marshaled  into  classes,  genera,  and  species,  just  as  the 
beings  of  the  present  are.  Palaeontology  is  the  name 
which  is  given  to  this  science  of  the  fossils.  It  is  a  word 
derived  from  three  Greek  words — palaios,  ancient;  ontos, 
the  genitive  of  the  word  for  being ;  and  logos,  discourse. 
It  is  really  the  application  of  two  sciences,  botany  and 
zoology,  to  the  remains  of  life  left  by  the  past.  Some, 
however,  use  the  term  in  a  more  restricted  sense,  consid- 
ering it  as  meaning  the  science  of  fossil  animals,  while 
the  term  Fossil  Botany  is  applied  to  the  science  of  fossil 
plants. 

248.  Living  Structures  of  Former  Ages  like  those  of 
the  Present. — Vegetables  and  animals  were  constructed 
on  the  same  fundamental  plans  in  the  far  past  that  they 
are  now.  The  same  general  divisions  existed.  And  the 
differences  result  from  variations  which  were  made  to 
meet  different  circumstances,  and  not  from  any  essential 
alterations  in  general  plans.  This  being  the  case,  it  is 
appropriate,  before  we  go  farther,  to  look  at  the  outlines 
of  the  Creator's  plans  in  the  construction  of  the  forms 
of  vegetable  and  animal  life.  A  knowledge  of  them  will 
aid  you  materially  in  following  out  the  developments 
which  I  shall  make  to  you  in  the  succeeding  chapters,  in 


RECORD    OF   LIFE   IN   THE   HOCKS. 


165 


regard  to  the  different  ages  of  the  earth's  progress  or 
growth. 

249.  Amphigens. — The  vegetable  world  presents  to  us 
five  groups,  marked  by  different  modes  of  growth.  First 
we  have  the  amphigens,  so  named  because  they  increase 
by  growth  on  all  sides,  the  name  being  derived  from  two 
Greek  words,  amphi,  around,  and  gennao^  to  produce. 
This  mode  of  growth  can  be  seen  in  the  lichens  that 
spread  out  upon  the  surfaces  of  rocks,  and  trunks  of 
trees,  and  old  fences.  This  division  includes,  besides 
these  lichens,  tho  scum-like  growths  that  you  see  on 
stagnant  water  (Confervse),  the  mushroom  family  (Fun- 
gi), and  the  sea- weeds  (Algae)  that  lie  upon  the  shelves 
and  ledges  of  the  shallow  places  in  the  sea.  These  are 
all  represented  in  Fig.  85.  They  are  the  lowest  kinds  of 


Fig.  85. 


vegetation,  and  are  found  where  no  other  plants  can 
grow.  They  may  be  considered  as  pioneers  of  the  higher 
orders  of  plants,  helping  to  weather  the  rock,  and  to 
gather  upon  it  the  material  for  the  growth,  in  time,  of 


l'~  GEOLOGY. 

other  plants,  and  enriching  also  barren  soils  by  their  de- 
cay, so  as  to  prepare  them  for  higher  forms  of  vegeta- 
tion. These  plants  are  wholly  cellular  in  their  composi- 
tion, while  all  other  plants,  as  grasses,  trees,  and  shrubs, 
have  tubular  vessels  for  the  circulation  of  the  sap.  The 
latter  are  called,  therefore,  vascular  plants,  and  the  for- 
mer cellular. 

250.  Acrogens. — This  division  includes  the  mosses,  the 
ferns,  the  horsetails,  and  the  ground-pine  family.     These 
plants  are  pictured  in  Fig.  86,  the   tall  tree-fern  that 
grows  in  tropical  climates  being  represented  as  well  as 
the  common  fern,  or  brake,  that  is  so  familiar  to  us  in 
temperate  climates.     The  plants  of  this  class  delight  in 
swamps  and  shady  places.     Their  remains  are  found  in 
the  peat  of  the  present  day,  and  in  the  coal  deposits  of 
past  ages.     Their  title  comes  from  the  fact  that  they  in- 
crease from  the  top  alone,  it  being  derived  from  two 
Greek  works,  cikros,  summit,  and  gennao.     These,  like 
the  amphigens,  are  of  service  in  preparing  soil  for  the 
nourishment  of  higher  orders  of  plants.    They  do  a  great 
work  in  this  respect,  because  they  have  a  rapid  growth, 
and  from  year  to  year,  by  their  decay,  add  to  the  solid, 
nutritious  material  in  the  swamps  and  damp  places  where 
they  so  luxuriantly  flourish.    Neither  the  amphigens  nor 
the  acrogens  aiford  support  to  animal  life  to  any  extent. 

251.  Gymnogens. — In  this  group,  Fig.  87  (p.  168),  we 
have  the  cycads,  or  pineapple  family,  and  the  first  pines, 
or  cone-bearing  trees  (conifers).     They  have  this  name 
(gymnos,  naked,  and  gennao)  because  their  seeds  are 
naked  instead  of  being  inclosed  in  cases.     They  appear 
in  various  kinds  of  soil,  the  dry  as  well  as  the  damp. 
From  them,  like  the  acrogens,  peat  and  coal  have  been 
largely  formed.     Our  coal,  both  bituminous  and  anthra- 
cite, was  laid  down  in  beds  from  the  growth  of  both 
acrogens  and  gymnogens  far  back  in  the  past,  as  you 
will  see  in  another  chapter.     Their  stiff,  juiceless  leaves, 
scaly  seeds,  and  hard  berries  afford  but  little  nutriment 


KECORD    OF  LIFE   IN   THE 


Fig.  86. 


for  animals,  and  therefore  the  record  of  the  rocks  shows 
but  scanty  remains  of  any  of  the  higher  orders  of  ani- 
mals amid  those  of  these  plants.  The  inference  is  a  clear 
one  that  when,  in  the  ages  past,  these  vegetables  were 


103 


GEOLOGY. 


Fig.  87. 

made  to  flourish  for  special  purposes,  but  few  of  the  ani- 
mals of  higher  orders  were  brought  upon  the  scene,  be- 
cause there  was  little  food  which  such  animals  could  ap- 
propriate to  themselves.  The  principle  of  adaptation 
was  applied  to  the  mutual  relations  of  the  vegetable  and 
animal  worlds  in  those  ages  as  thoroughly  as  now  by  an 
all- wise  and  omnipotent  Creator. 

252.  Endogens. — In  this  division  of  plants  we  have  the 
grasses,  rushes,  lilies,  canes,  and  palms,  as  exhibited  in 
Fig.  88.  Here  we  have  a  decided  advance  on  the  pro- 


RECORD    OF   LIFE   IN   THE    HOCKS. 


169 


Fig.  88. 

viously  mentioned  groups  in  the  objects  which  the  Crea- 
tor had  in  view  in  introducing  them.  While  the  plants 
of  this  class,  like  those  of  the  former  classes,  add  by  their 
decay  to  the  nutritious  material  of  the  soil,  their  chief 
design  is  to  afford  nutrition  directly  to  the  animal  king- 
dom. What  was  in  the  other  classes  only  an  incidental 
object,  is  in  this  the  primary  one,  while  the  primary  of 
those  classes  is  here  the  incidental.  The  chief  object  of 

H 


170 


GEOLOGY. 


the  ainphigens,  gymnogens,  and  acrogens  was  to  build 
up,  as  we  may  say,  the  soil  of  the  earth,  and  of  a  part  of 
them  to  furnish  the  coal  which  has  been  stored  up  for 
the  use  of  man.  They  are  geological  in  their  agency — 
that  is,  earth-making.  But  the  chief  object  of  the  endo- 
gens  has  been  to  furnish  food  to  animals — that  is,  animal- 
making.  They  are  zoological  in  their  agency.  The  name 
endogens  comes  from  endon,  within,  and  gennao,  and 
expresses  the  fact  that  the  growth  is  by  addition  in  all 
the  parts  of  the  plant  equally.  In  the  trunk  or  stem,  for 
example,  there  is  in  every  addition  a  formation  of  new 
fibres  intermingled  with  those  already  present,  and  in  old 
trunks  or  stems  the  hardest  part  of  the  wood  is  toward 
the  surface,  and  the  softest  toward  the  centre.  Endoge- 
nous plants  have  no  pith  and  no  distinct  bark. 

253.  Exogens. — This  name  comes  from  ex,  out,  and 
gennao.  It  indicates  an  entirely  different  mode  of  growth 
from  that  of  the  endogens.  There  is  a  pith  and  distinct 
bark,  and  the  addition  is  in  rings  outside  of  those  which 
are  already  formed,  the  hardest  part  being  toward  the 
centre,  and  the  softest  toward  the  surface.  The  differ- 
ence in  the  modes  of  growth  in  the  endogens  and  exo- 
gens  is  exhibited  by  sections  of  stems  or  trunks  in  Figs. 

89  and  90.  In  the 
endogenous  stem, 
Fig.  89,  you  see 
the  holes  occasion- 
ed by  the  section 
of  the  circulating 
vessels,  and  be- 
tween these  is  the 
mass  of  woody  or 
cellular  tissue  which  makes  up  the  substance  of  the  stem, 
and  forms,  indeed,  the  walls  of  the  vessels  themselves. 
But  in  the  exogenous  stem  you  see  the  pith,  the  rings 
of  wood,  and  the  bark.  The  lines  which  radiate  like  the 
spokes  of  a  wheel  from  the  pith  to  the  bark  are  called 


Fig;  89. 


Fig.  90. 


RjfiCOED    OF   LIFE   IN   THE   EOCKS. 


171 


medullary  rays,  and  indicate  plates  of  cellular  or  woody 
substance.  These  make  what  is  called  the  silver  grain 
of  the  wood.  This  division  of  plants  includes  the  herbs, 
shrubs,  and  timber  trees,  as  they  are  seen  grouped  in 


Fig.  91. 


In  this  and  Fig.  88  you  see  the  differences  be- 


Fig.  91. 


tween  the  two  classes  of  plants  exhibited  in  the  trunks 
of  two  trees  represented  as  cut  square  off.  The  same 
can  be  said  of  the  exogens  as  was  said  of  the  endogens 
in  relation  to  their  zoological  character.  The  remains  of 


172 


GEOLOGY. 


few  of  either  class  are  found  among  the  fossils  of  the  far 
past,  but  the  record  of  life  in  the  rocks  shows  that  they 
were  more  and  more  introduced  the  nearer  we  come 
down  to  the  age  of  man  in  tracing  the  successive  ages. 

254.  Investigation  of  Vegetable  Fossils. — We  can  not 
study  fossil  botany  in  the  same  manner  that  we  do  the 
botany  of  the  present.  In  the  latter  case  we  have  all  the 
parts  of  plants  in  full,  but  in  the  former  merely  remains, 
and  sometimes  only  scanty  ones.  In  many  cases,  there- 
fore, in  fossil  botany  we  can  only  approximate  to  a^true 
classification.  With  the  scanty  evidence  often  present- 
ed, it  is  not  surprising  that  some  mistakes  should  have 
been  made»  One  of  these  I  will  mention.  For  a  long 
time  certain  trunks  of  trees  found  in  the  coal  measures 
were  put  in  a  different  family  from  certain  roots  found 
also  in  these  measures ;  but  at  length  it  was  discovered 
that  the  roots  and  the  trunks  belonged  to  the  same  tree, 

though  in  the  stra- 
ta they  were  found 
separated  from  each 
other.  Of  the  many 
points  of  distinction 
in  regard  to  vegeta- 
ble fossils  I  will  no- 
tice but  one,  the  ve- 
nation  of  leaves, 
or  the  mode  of  dis- 
tribution of  their 
veins.     The  veins 
in  the  leaves  of  en- 
dogenous    plants 
run  parallel  with 
each  other,  as  seen 
in  Fig.  92,  while  in 
"V      the  exogenous  the 

veins  interlace,  as  seen  in  Fig.  93,  which  represents  the 
leaf  of  the  apple.  .  ^ 


RECORD    OF   LIFE   IN   THE   ROCKS.  173 

255.  Animal  Fossils. — The  study  of  fossil  zoology  is 
more  satisfactory  than  that  of  fossil  botany,  for  three 
reasons.     First,  the  distinctions  between  different  kinds 
of  animals  are  more  readily  made  out  from  the  partial  re- 
mains which  the  rocks  present  to  us.     The  reason  is  that 
the  differences  between  animals  are  of  a  more  decided 
character,  and  especially  those  which  mark  the  grand  di- 
visions into  classes,  as  you  will  soon  see.    Secondly,  most 
animal  remains  are  in  a  better  state  of  preservation  than 
vegetable  remains.    Shells,  corals,  scales,  teeth,  and  bones 
are  very  durable.     Thirdly,  more  attention  has  been  paid 
to  fossil  zoology  than  to  fossil  botany  by  geological  ob- 
servers. 

256.  Protozoans. — This  term,  derived  from  two  Greek 
words,  protos,  first,  and  zoon,  animal,  is  applied  to   a 
class   of  organisms  which  seem  to  stand  on  doubtful 
ground,  being  half  vegetable  and  half  animal  in  their 
characteristics.     They  are  the  sponges,  the  foraminifera, 
and  the  infusoria.     They  have,  for  the  most  part,  an  in- 
distinct organization,  so  that  they  can  not  be  classified 
with  any  of  the  great  divisions  of  the  animal  kingdom. 
Professor  Dana  therefore  speaks  of  them  as  systemless ; 
that  is,  as  belonging  to  no  system.     And  yet  it  would 
seem  as  if  some  of  them  have  a  sufficiently  definite  form 
to  be  classified,  as  operculina, /",  polymorphina,  g,  and 
nummulites,  #,  in  Fig.  83,  which  are  certainly  very  much 
like  ordinary  shell-fish,  though  their  resemblance  in  cer- 
tain respects  to  polypes  may  render  it  improper  to  lo- 
cate them  with  shell-fish  in  a  definite  classification.    The 
sponges  have  been  thought  by  some  to  be  on  doubtful 
ground,  but  it  is  now  considered  settled  that  they  are 
animal.     The  flinty  diatoms,  on  the  other  hand,  as  stated 
in  §  240,  are  now  to  be  placed  among  vegetable  organ- 
isms, and  are  not,  therefore,  any  longer  to  be  called  ani- 
malculaa. 

I  pass  now  to  the  consideration  of  those  animals  that 
can  be  definitely  classed  in  systems. 


174 


GEOLOGY. 


257.  Radiates. — This  class  includes  the  coral  animals, 
hydras,  sea-anemones,  sea-nettles,  echini,  or  sea-urchins, 
and  star-fishes.  The  name  comes  from  the  ray-like  ar- 
rangement which  is  so  manifest  in  many  of  these  ani- 
mals, and  exists  really  in  all.  It  is  from  this  radiate 
form  chiefly  that  many  of  them  were  formerly  supposed 
to  be  plants,  and  even  now  they  are  often  called  plant- 
animals.  Examples  of  them  are  seen  in  Fig.  94.  Here 


Fig.  94. 


are  represented  the  star-fish,  the  little  hydra,  a  medusa, 
a  sea-urchin,  and  sea-anemones.  One  of  the  anemones  is 
divided  in  half,  that  you  may  see  the  interior.  They  are 
all  inhabitants  of  the  ocean,  and  many  of  them,  as  they 
are  seen  sometimes  clustered  together  over  a  considera- 
ble space,  present,  with  their  beautiful  and  varied  colors, 
the  appearance  of  a  garden  under  water.  They  are 


RECORD    OF   LIFE    IN   THE    ROCKS. 


175 


pulpy  in  their  consistence,  many  of  them,  however,  hav- 
ing a  hard  frame-work,  as  the  coral  animals  and  the  star- 
fishes. They  live  to  a  great  extent  on  the  microscopic 
organisms  which  abound  in  the  sea;  and,  though  they  are 
more  zoological  than  the  protozoans,  they  are  largely  ge- 
ological^ especially  the  coral  animals,  which  have  con- 
tributed, and  still  contribute,  as  you  have  seen  (§  236), 
such  quantities  of  limestone  to  the  earth-making  pro- 
cesses. 

258.  Mollusca. — This  class,  Fig.  95,  contains  animals 


Fig.  95. 


of  a  much  more  complicated  and  varied  character  than 
the  preceding.    They  are  not  confined  to  the  ocean,  but 


176  GEOLOGY. 

many  live  in  lakes,  rivers,  and  swamps,  and  some  even 
on  the  dry  land.  The  substance  of  these  animals  is  soft, 
as  seen  in  the  common  oyster,  and  hence  the  name,  which 
comes  from  the  Latin  mollis,  soft.  But  most  of  them 
have  hard  shells,  and  so  are  called,  in  common  language, 
shell-fish ;  though  some,  as  the  slugs,  are  wholly  uncov- 
ered. This  class  includes  oysters,  mussels,  clams,  snails, 
slugs,  nautili,  cuttle-fishes,  etc.  The  shells  of  some  of 
these  animals  have  contributed  largely  to  the  formation 
of  the  limestone  of  the  earth,  but  they  are  more  zoolog- 
ical in  their  relations  than  the  previous  class.  So  widely 
distributed  have  shell-fish  always  been,  and  so  durable 
are  their  shells,  that  their  fossils  are  of  great  use  to  the 
geologist  in  determining  the  relative  ages  of  the  rocks. 

259.  Articulata. — This  sub-kingdom  includes  insects, 
worms,  the  spider  and  scorpion  tribe,  and  the  crab  tribe. 
These  varieties  are  represented  in  Fig.  96.     You  have 
here  animals  of  extremely  various  character  in  many  re- 
spects.    Nothing,  for  example,  could  be  more  unlike 
than  a  butterfly  and  a  lobster.     Yet  all  these  varieties 
agree  in  one  thing — in  having  a  covering  which  answers 
to  them  as  a  skeleton,  in  giving  firmness  to  the  body, 
and  furnishing  points  of  attachment  to  their  muscles. 
This  is  very  obvious  in  such  animals  as  crabs  and  lob- 
sters, but  it  is  equally  true  of  insects  and  worms.     This 
skeleton  coat  of  mail,  as  it  may  be  called,  has  commonly 
a  very  manifest  ring-like  arrangement ;  and,  as  the  rings 
are  jointed  with  each  other,  the  name  articulata,  coming 
from  the  Latin  articulus,  joint,  is  given  to  this  division 
of  the  animal  kingdom.     The  articulata  are  mostly  zoo- 
logical in  their  relations,  and  are  only  slightly  geological. 
They  live  in  every  element — in  the  air,  the  earth,  and 
the  water.     Some  are  animal-eaters,  some  vegetable-eat- 
ers, and  some  both,  and  they,  in  their  turn,  are  the  food 
of  other  animals  of  various  kinds. 

260.  Vertebrata. — The  animals  of  this  sub-kingdom 
have  an  internal  skeleton  with  a  back-bone,  so  called  in 


EECOED    OF   LIFE   IN   THE   ROCKS. 


177 


Fig.  96. 

common  language,  made  up  of  vertebrae.*    Through  this 
chain  of  bones  runs  a  nervous   extension  of  the  brain 
called  the  spinal  marrow,  from  which  nerves 
branch  out  to  different  parts  of  the  body.     In 
Fig.  97  you  see  represented  a  single  vertebra 
from  the  spinal  column  or  back-bone  of  man, 
a  being  its  front  part,  and  b  its  pointed  rear 
Fig.  97.      part,  which  you  feel  on  tracing  the  line  of  the 

*  Sometimes  animals  are  spoken  of  as  being  in  two  great  classes, 
the  Vertebrates  and  the  Invertebrates,  those  which  have  and  those 
which  have  not  vertebrae,  the  prefix  in  being  a  particle  of  negation. 
The  Invertebrates  include  the  three  great  classes  already  spoken  of— 
Radiates,  Mollusks,  and  Articulates. 

H2 


178. 


GEOLOGY. 


back-bone.  You  see  the  opening  which 
is  filled  with  the  spinal  marrow.  In 
Fig.  98  you  see  the  brain  and  spinal 
marrow  of  man,  showing  how  the  nerves 
branch  out  from  the  spinal  marrow  in 
the  vertebral  column.  This  column  dif- 
fers much  in  length  and  arrangement 
in  different  animals,  being,  for  instance, 
vastly  longer  in  the  serpent  tlian  in  man, 
and  having  a  number  of  vertebrae  in  pro- 
portion to  its  length.  The  vertebrata 
have  four  grand  divisions — mammals, 
or  those  that  suckle  their  young,  birds, 
reptiles,  and  fishes.  These  are  repre- 
sented in  Fig.  99.  For  the  most  part, 
it  is  in  this  sub-kingdom  that  we  have 
the  greatest  complication  of  structure, 
and  with  it  the  highest  manifestations 
of  life.  Intellectual  qualities  appear 
here  with  their  greatest  prominence, 
especially  in  those  portions  that  ap- 
proach to  man;  and  in  man,  the  highest 
of  mammals,  not  only  is  there  superior- 
ity in  degree  of  intellect,  but  there  are 
superadded  powers,  making  his  intel- 
lect different  in  kind  as  well  as  in  de- 
gree, thus  linking  him  with  the  Infinite,  and  showing  the 
significance  of  the  expression,  made  in  the  image  of 
God.  Little  have  the  vertebrata  contributed  of  material 
for  earth-making,  but  they  are  almost  wholly  zoological 
in  their  relations,  presenting  in  this  respect  an  extreme 
contrast  to  the  lower  orders  of  animal  life,  the  protozo- 
ans and  the  radiates.  The  relations  of  the  vertebrates 
and  the  higher  orders  of  the  vegetable  world,  the  endo- 
gens  and  the  exogens,  are  very  obvious,  and  accordingly 
we  find  in  the  life-record  of  the  rocks  the  evidence  of 
their  introduction  together  upon  the  world's  arena,  the 


i 

tig.  08. 


RECORD    OF   LIFE   IN   THE   ROCKS. 


179 


Fig.  99. 

full  introduction   of  both  being  reserved  for  the  age 
which  ushered  in  the  advent  of  man. 

261.  Divisions  of  the  Earth's  History.— As  the  record 
of  the  rocks  is  a  life-record,  it  seems  eminently  proper 
to  base  the  division  into  ages  upon  the  changes  which 
we  find  in  the  forms  of  life  from  age  to  age.  There  are 
other  modes  of  division ;  but,  as  the  developments  of 
the  life-record  have  come  out,  the  tendency  has  been 
more  and  more  to  a  division  on  this  basis.  This  division 
has  been  made  differently  by  different  authors.  The  one 
which  I  shall  follow  is  that  which  is  brought  out  in  that 
grand  American  work,  Dana's  Geology.  He  divides  the 
geological  history  of  the  world  into  seven  periods :  the 
Azoic  age,  in  which  there  was  no  life  (a  privative,  and 
zoe,  life) ;  the  age  of  Mollusks ;  the  age  of  Fishes ;  the 
age  of  Coal-plants,  or  the  Carboniferous  age ;  the  age  of 
Reptiles ;  the  age  of  Mammals ;  and  the  age  of  Man. 


180  GEOLOGY. 

The  last  age  is  still  in  progress ;  the  others  are  in  the 
past.  How  long  they  were  we  know  not;  but  that  they 
were  each  much  longer  than  the  age  of  man  has  thus  far 
been  we  have  the  most  conclusive  evidence  to  show. 

It  is  proper  to  notice  here  a  division  of  time  into  five 
periods  which  is  common  in  works  on  Geology,  and  in 
relation  to  which  there  are  certain  terms  that  are  in  con- 
stant use  by  all  geologists.  1.  Azoic  time.  This  has 
been  already  explained.  2.  Palceozoic  time.  This  was 
a  period  in  which  the  forms  of  life,  as  their  remains 
show,  were  very  ancient — that  is,  differing  decidedly 
from  the  present.  This  period  includes  the  three  ages  of 
mollusks,  of  fishes,  and  of  coal-plants.  Its  name  comes 
from palaios,  old,  and  zoe.  3.  Mesozoic  time,  the  fossils 
of  which  differ  less  than  those  of  the  Paleozoic  from  the 
living  forms  of  the  present,  the  term  being  derived  from 
mesos,  middle,  and  zoe.  The  ages  included  in  this  period 
are  the  middle  ages  of  geological  history,  and  cover 
what  is  called  the  age  of  Reptiles,  which  is  really,  like  all 
the  other  grand  divisions  of  geological  time,  a  succession 
of  long  ages.  4.  Cainozoic  (or,  as  it  is  sometimes  called, 
Cenozoic)  time,  from  Jcainos,  recent,  and  zoe.  This  is 
the  age  of  Mammals.  5.  The  Present  age.  The  terms 
primary,  secondary,  and  tertiary  are  used  often  as  mean- 
ing the  same,  respectively,  as  Paleozoic,  Mesozoic,  and 
Cainozoic. 

262.  Boundaries  of  the  Ages. — No  age  has  had  a  sharp- 
ly-defined limit  in  relation  to  its  life-record,  but  each 
age  has  been  to  some  extent  mingled  with  other  ages — 
in  its  rise  with  the  age  that  preceded  it,  and  in  its  de- 
cline with  the  age  that  followed  it.  Geological  history, 
as  Professor  Dana  remarks,  is  like  human  history  in  this 
respect,  ages  in  both  cases  being  marked  by  peculiarities 
which,  indistinct  at  first  and  foreshadowed  in  a  previous 
age,  at  length  come  out  prominently  to  view.  When 
they  thus  culminate  it  is  easy  to  trace  them  back  to  their 
rise,  and  follow  their  growth,  and  then  their  decline,  as 


AZOIC   AGE.  181 

they  lose  themselves  in  the  rising  peculiarities  of  another 
coming  period  or  age.  Thus  that  remarkable  age,  the 
coal-bearing  or  Carboniferous  age,  which  was  specially 
occupied  in  making  and  storing  up  coal  in  the  strata  of 
the  earth's  crust,  was  foreshadowed  by  the  occurrence 
of  plants  similar  to  the  coal-plants  in  the  previous  age, 
the  age  of  Fishes.  So  also  mammals  appeared  to  some 
extent  long  before  that  age  in  which  these  animals  were 
so  numerous,  in  many  cases  so  monstrous,  as  to  make  it 
proper  to  denominate  it  the  age  of  Mammals.  It  may  be 
remarked,  in  this  connection,  that  it  is  not  the  idea  to 
give  the  name  of  a  class  of  animals  to  an  age  because 
they  are  more  abundant  then  than  they  are  in  any  other 
age.  Thus  the  mollusks  are  really  not  as  abundant  in 
the  age  to  which  they  give  their  name  as  they  are  after- 
ward in  the  age  of  Reptiles,  but  in  the  age  of  Mollusks 
they  are  more  abundant  than  any  other  class.  At  the 
same  time,  abundant  as  are  the  mollusks  in  the  age  of 
Reptiles,  the  latter  then  surpass  them  in  abundance,  and 
so  give  the  name  to  the  age.  The  articulates,  which  do 
not  give  a  name  to  any  age,  have  steadily  increased  from 
their  small  beginning  far  back  at  the  conclusion  of  the 
Azoic  age  on  to  the  age  of  the  present. 


CHAPTER  XIII. 

AZOIC   AGE. 

263.  Beginning  of  Solidification  of  the  Earth. — There 
was  a  time  when  the  earth  was  a  liquid  mass.  Of 
course,  with  such  a  degree  of  heat  as  sufficed  to  maintain 
it  in  this  condition,  there  was  no  liquid  water,  but  the 
heated  ball  was  enveloped  in  steam.  But  after  a  time  a 
portion  of  the  outside  of  the  mass  became  solid,  forming 
a  crust.  Professor  Hitchcock  savs  that  it  is  not  unlike- 


1 82  GEOLOGY. 

ly  that  the  time  occupied  in  cooling  the  earth  from  its 
melted  state,  sufficiently  to  form  a  crust,  was  longer  than 
all  the  time  of  the  ages  which  were  occupied  in  laying- 
down  the  strata  that  contain  fossils — that  is,  longer  than 
all  paleozoic,  mesozoic,  and  cainozoic  time.  And  if  the 
earth,  as  is  supposed  by  many  geologists,  was  once  so 
heated  as  to  be  in  a  vaporous  state,  the  time  of  cooling 
must  have  been  vastly  longer  than  this.  But,  whether 
we  reckon  the  azoic  or  lifeless  age  of  the  earth  as  begin- 
ning with  the  first  solidification  of  the  crust,  or  with  the 
melted  state,  or  extend  it  back  to  the  supposed  vaporous 
or  nebulous  state,  so  called,  the  time  that  elapsed  before 
any  life  appeared  on  the  earth  was  immense  in  length. 

264.  Floor  of  the  Earth's  Crust. — It  was  in  the  solidifi- 
cations  of  the  Azoic  age  that  the  floor,  as  we  may  term 
it,  of  the  earth's  crust  was  laid.     This  floor  lies  over  the 
melted  matter  which  is  inclosed  still  within  the  crust,  and 
which  constitutes  by  far  most  of  the  bulk  of  the  globe. 
It  is  not  an  even  floor,  although  it  was  laid  down  in  hor- 
izontal strata.     It  has  been  bent,  and  folded,  and  frac- 
tured, and  lifted  up,  and  broken  through  by  melted  mass- 
es forced  upward  from  below.    Although,  then,  its  stra- 
ta were  laid  before  any  of  the  fossiliferous  strata,  yet, 
from  these  bendings  and  upheavals,  they  appear  in  some 
parts  of  the  earth  upon  the  surface  of  its  crust,  the  fos- 
siliferous rocks  skirting  their  prominences  or  partially 
overlying  them. 

265.  Changes  in  the  Azoic  Rocks.— Vast  changes  oc- 
curred in  the  azoic  rocks  during  both  the  Azoic  age  and 
the  succeeding  ages,  for  fire  and  water  were  at  work 
upon  them  more  or  less  during  all  that  time.     Just  as 
soon  as  solidification  took  place  on  the  surface  of  the 
great  melted  ball  which  once  constituted  our  earth,  a 
large  part  of  the  steam  surrounding  it  was  condensed 
into  water,  which  of  course  fell  in  rain.     At  the  same 
time,  the  forming  crust,  as  is  the  case  with  all  matter  ex- 
cept water,  in  passing  from  the  melted  to  the  solid  state, 


AZOIC   AGE.  183 

contracted,  and  this  contraction  crumpled  it  into  folds, 
regular  and  irregular,  and  thus  made  channels  and  cavi- 
ties for  the  water  to  run  and  dash  in.  Water  then  be- 
gan that  great  work  of  denudation,  which,  as  you  have 
seen  in  previous  parts  of  this  book,  it  has  been  carrying 
on  ever  since.  From  that  denudation  in  this  first  age 
of  the  world  was  supplied  material  for  the  strata  of  the 
grand  azoic  floor,  which  covers  up  the  fiery  deeps  with- 
in, and  upon  and  against  which  the  rocks  of  after  ages 
were  laid.  So  great  have  been  the  changes  in  the  azoic 
rocks,  that  it  is  impossible  to  distinguish  among  them 
any  that  can  with  certainty  be  made  out  to  be  portions 
of  the  original  crust — that  is,  portions  of  the  first  solidi- 
fication. 

266.  Some  of  the  present  Land  formed  in  the  Azoic 
Age. — In  some  quarters  of  the  earth  the  azoic  rocks  ap- 
pear upon  the  surface  of  the  earth's  crust.     These,  as 
Professor  Dana  states,  are  "either,  1.  Those  which  have 
always  remained  uncovered ;  2.  Those  which  have  been 
covered  by  later  strata,  but  from  which  these  superim- 
posed beds  have  been  simply  washed  away  without  much 
disturbance ;  3.  Those  once  covered,  like  the  last,  but 
which,  in  the  course  of  the  upturnings  of  mountain-mak- 
ing, have  been  thrust  upward  among  the  displaced  stra- 
ta, and  in  this  way  have  been  brought  out  to  light."    The 
areas  in  which  the  rocks  appeared  above  the  surface  of 
the  water  during  the  Azoic  age  were  scanty  compared 
with  the  whole  area  occupied  by  the  land  at  the  present 
time.     These  areas  were  the  beginnings  of  the  conti- 
nents, and  it  was  by  successive  additions  to  them  during 
the  succeeding  ages  that  the  continents  grew  to  be  what 
they  now  are. 

267.  America  and  Europe  in  the  Azoic  Age. — The  azoic 
rocks  that  come  to  the  surface  in  North  America  occupy, 
for  the  most  part,  a  very  long  and  comparatively  narrow 
strip  of  land  extending  from  Nova  Scotia  west  to  the 
base  of  the  Rocky  Mountains.    This  monstrous  island 


184  GEOLOGY. 

was  not  straight,  but  bent  upward  either  way,  forming 
an  elbow,  and  shaped  much  like  Fig.  100.    If  you  corn- 


Fig.  100. 

pare  this  with  the  shape  of  North  America  as  a  whole, 
you  will  see  why  this  beginning  of  the  continent  had  this 
shape,  as  it  was  completed  afterward  by  additions.  The 
elbow  extends  downward,  as  the  lower  part  of  the  com- 
plete continent  does,  and  the  larger  limb  of  the  island 
corresponds  with  the  more  extended  side  of  the  conti- 
nent. Some  few  other  comparatively  small  azoic  areas 
are  found  in  North  America,  one  of  which  is  in  Missouri, 
and  includes  the  noted  Iron  Mountains.  All  else  was  sea 
in  that  quarter  to  the  end  of  the  Azoic  age.  Agassiz  says 
of  the  long  island  which  was  the  beginning  of  the  North 
American  continent,  "  We  may  still  walk  along  its  ridge, 
and  know  that  we  tread  upon  the  ancient  granite  that 
first  divided  the  waters  into  a  northern  and  southern 
ocean ;  and,  if  our  imaginations  will  carry  us  so  far,  we 
may  look  down  toward  its  base,  and  fancy  how  the  sea 
washed  against  this  earliest  shore  of  a  lifeless  world." 

Europe  was  quite  in  contrast  with  America  in  this  age. 
There  was  no  one  great  island,  but  several  of  considera- 
ble size,  and  some  small  ones  were  scattered  about  in  that 
part  of  the  vast  azoic  ocean.  There  was  no  so  obviously 
marked  beginning  of  a  continent  as  in  the  case  of  North 


AZOIC   AGE.  185 

America.  It  is  with  great  truth,  then,  that  Agassiz  says 
that,  though  America  is  called  the  New  World,  she  is 
really  the  Old  World,  for  she  is  really  first-born  among 
continents. 

268.  Thickness  of  the  Azoic  Strata. — The  strata  of  the 
azoic  rocks  varies  from  twenty  to  thirty  thousand  feet  in 
thickness.     An  immensely  long  period  was  required  to 
deposit  and  solidify  so  much  material,  and  comparative 
quiet  must  have  reigned  during  their  deposit.     The  up- 
heavals occurred  after  this  was  done. 

269.  Upheavals  and  Bendings. — These  are  very  exten- 
sive, and  there  is  much  regularity  in  them,  for  the  strike 
is  the  same  in  some  cases  over  great  extents  of  territory. 
The  regularity  is  most  observable  in  the  strata  of  the  lat- 
ter part  of  the  age,  for  in  the  first  part  the  heat  was  so 
great  that  the  rocks  then  formed  are  much  contorted. 

270.  Rocks  of  the  Azoic  Age. — The  rocks  of  this  age 
are  granite,  gneiss,  schists,  limestones,  etc.     They  were 
mostly  deposited  in  beds,  and  then  were  crystallized 
chiefly  by  the  influence  of  the  great  heat  which  pre- 
vailed in  that  age.     Some  of  the  granite  is  metamorphic, 
but  some  of  it  was  made  originally  as  granite,  having 
been  forced  upward  from  below,  as  was  often  done  at 
different  periods  in  the  succeeding  ages.     One  character- 
istic of  the  azoic  rocks  is  the  prevalence  of  iron.     Some 
of  the  minerals  which  enter  into  the  composition  of  some 
of  the  rocks  contain  iron,  and  there  are  sometimes  found 
in  the  strata  beds  of  iron  ore  of  greater  extent  than  in 
any  other  age. 

271.  Heat  and  Light  in  the  Azoic  Age.  —  The  heat  of 
the  forming  crust  in  the  first  part  of  this  age  must  have 
been  very  great,  and  the  upheavings  and  commotions 
must  then  have  been  tumultuous.     Hugh  Miller  thus  de- 
scribes what  may  be  imagined  to  be  the  state  of  things 
at  that  time.     "  Let  us  suppose  that  during  the  earlier 
part  of  this  period  of  excessive  heat  the  waters  of  the 
ocean  had  stood  at  the  boiling  point  even  at  the  surface, 


186  GEOLOGY. 

and  much  higher  in  the  profounder  depths ;  and  farther, 
that  the  half-molten  crust  of  the  earth,  stretched  out  over 
a  molten  abyss,  was  so  thin  that  it  could  not  support, 
save  for  a  short  time,  after  some  convulsion,  even  a  small 
island  above  the  sea  level.  What,  in  such  circumstances, 
would  be  the  aspect  of  the  scene,  optically  exhibited 
from  some  point  in  space  elevated  a  few  hundred  yards 
over  the  sea  ?  It  would  be  simply  a  blank,  in  which  the 
intensest  glow  of  fire  would  fail  to  be  seen  at  a  few  yards' 
distance.  An  inconsiderable  escape  of  steam  from  the 
safety-valve  of  a  railway  engine  forms  so  thick  a  screen 
that,  as  it  lingers  for  a  moment,  in  the  passing,  opposite 
the  carriage  windows,  the  passengers  fail  to  discern 
through  it  the  landscape  beyond.  A  continuous  stra- 
tum of  steam,  then,  that  attained  to  the  height  of  even 
our  present  atmosphere,  would  wrap  up  the  earth  in  a 
darkness  gross  and  palpable  as  that  of  Egypt  of  old — a 
darkness  through  which  even  a  single  ray  of  light  would 
fail  to  penetrate.  And  beneath  this  thick  canopy  the 
unseen  deep  would  literally  "  boil  as  a  pot"  wildly  tem- 
pested below;  while  from  time  to  time,  more  deeply 
seated,  would  upheave  suddenly  to  the  surface  vast 
tracts  of  semi-molten  rock,  soon  again  to  disappear,  and 
from  which  waves  of  bulk  enormous  would  roll  outward, 
to  meet  in  wild  conflict  with  the  giant  waves  of  other 
convulsions,  or  to  return  to  hiss  and  sputter  against  the 
intensely -heated  and  fast-foundering  mass,  whose  violent 
upheaval  had  first  elevated  and  sent  them  abroad."  At 
length,  however,  the  earth's  forming  crust  would  cool 
down,  so  that  the  steam  atmosphere  would  become  less 
thick,  and  after  a  time  the  rays  of  the  sun  would  strug- 
gle through,  forming  at  first  a  faint  twilight,  but  gradu- 
ally strengthening  as  the  age  advanced.  At  its  close, 
"  day  and  night — the  one  still  dim  and  gray,  the  other 
wrapped  in  a  pall  of  thickest  darkness — would  succeed 
each  other  as  now,  as  the  earth  revolved  on  its  axis,  and 
the  unseen  luminary  rose  high  over  the  cloud  in  the  east, 


AGE    OF   MOLLUSKS.  187 

or  sunk  in  the  west  beneath  the  undefined  and  murky 
horizon."  So  great  was  the  heat  that  prevailed  while 
the  azoic  strata  were  laid  down  that  it  does  not  seem 
strange  that  no  remains  of  life  are  found  in  them.  "As 
well,"  says  Agassiz,  "might  we  expect  to  find  the  re- 
mains of  fish,  or  shells,  or  crabs  at  the  bottom  of  geysers 
or  of  boiling  springs,  as  on  those  early  shores,  bathed  by 
an  ocean  of  which  the  heat  must  have  been  so  intense." 
272..  State  of  the  Surface  at  the  End  of  this  Age. — At 
the  end  of  the  Azoic  age  there  was  nothing  like  the  di- 
versity of  surface  that  there  is  at  the  present  time,  there 
being  no  high  elevations  over  the  comparatively  small 
portions  of  land  which  then  rose  above  the  level  of  the 
universal  ocean.  Still,  denudation  had  been  going  on 
during  all  the  progress  of  the  age,  and  there  were  there- 
fore extensive  areas  where  there  were  gravel,  sand,  and 
some  material  ground  up  so  fine  as  to  be  mud.  This 
broken  and  ground  material  was  spread  not  only  here 
and  there  over  the  land,  but  over  the  bottom  of  the  seas 
as  now.  In  short,  the  earth  was  prepared  for  the  com- 
ing life  of  the  next  age.  A  part  of  this  preparation  was 
the  reduction  of  the  temperature  to  such  a  point  as  was 
consistent  with  the  existence  of  plants  and  animals. 


CHAPTER  XIV. 

AGE    OF   MOLLUSKS,  OE   SILURIAN  AGE. 

273.  Dawn  of  Life. — The  earth  having  been  prepared 
during  the  Azoic  age  for  vegetation,  life,  both  vegetable 
and  animal,  was  now  introduced  upon  the  scene.  That 
its  introduction  occurred  at  that  time  is  inferred  from 
the  fact  that  the  beginning  of  the  life-record  is  found  in 
the  rocks  that  were  then  formed,  or,  in  other  words,  that 
no  fossils,  no  remains  of  life,  have  been  found  in  the 
rocks  that  were  formed  previous  to  that  period.  There 


188  GEOLOGY. 

are,  indeed,  certain  contents  of  rocks  of  the  Azoic  age, 
from  which  some  have  argued  that  there  were  both  veg- 
etables and  animals  in  existence  then,  and  that  they  were 
so  acted  upon  by  the  mechanical  and  chemical  agencies 
of  that  early  period  that  we  now  find  only  what  was 
produced  from  them.  This  supposition  may  possibly  be 
correct.  If  so,  we  have  an  example  of  that  foreshadow- 
ing that  I  spoke  of  in  §  262,  the  scanty  life  of  the  one 
age  in  this  case  preceding  the  full  introduction  of  life  in 
the  other.  But,  at  whatever  time  life  was  introduced,  it 
was  done  by  a  distinct  exertion  of  creative  power.  It 
was  no  result  of  chemical  or  mechanical  forces  already 
existing,  foivdead  matter  has  no  disposition  or  tendency 
in  itself  to  produce  the  seed  of  a  vegetable  or  the  germ 
of  an  animal.  All  vegetables  and  animals  have  a  parent- 
age, and  the  beginnings  of  the  lines  of  succession  were 
products  of  creative  power.  In  other  words,  each  spe- 
cies, either  vegetable  or  animal,  was,  when  first  intro- 
duced upon  the  earth,  a  distinct  creation.  Though  the 
influence  of  circumstances  may  produce  varieties  in  any 
species,  no  species  can  be  derived  from  any  other  spe- 
cies. There  is  a  disposition  in  some  to  discard  this 
view.  They  seem  to  dislike  the  idea  of  a  present  deity, 
and  to  desire  the  removal  of  creative  power  as  far  back 
in  time  as  possible,  as  if  in  the  dim  distance  they  get  rid 
of  some  of  the  actual  force  of  the  power. 

274.  Rocks  of  this  Age. — The  rocks  are  of  considerable 
variety — hard  sandstones,  limestones,  slates,  shales,  flag- 
ging-stones, marls,  and  conglomerates.  Some  of  the  for- 
mations are  in  part  calcareous — that  is,  they  have  carbon- 
ate of  lime  mingled  with  other  materials ;  while  in  some 
formations  there  is  quite  pure  limestone,  which  in  some 
localities  has  been  converted  into  marble.  At  Niagara 
Falls  we  have  85  feet  of  limestone  lying  upon  80  of  shales, 
the  erosion  of  the  soft  shales  by  the  water  causing  a  con- 
stant undermining  of  the  hard  limestone,  and  therefore 
a  recession  of  the  falls  toward  Lake  Erie,  as  stated  in 
§183. 


AGE   OF   MOLLUSKS. 


189 


275.  Arrangement  of  the  Rocks. — The  arrangement  of 
the  rocks  of  this  age  was  first  thoroughly  observed  in  a 
region  of  the  western  part  of  England,  which  was  in  an- 
cient times  inhabited  by  a  tribe  called  the  Silures.  Hence 
this  age  is  often  called  the  Silurian  age,  and  the  rocks  are 
said  to  belong  to  the  Silurian  system,  no  matter  in  what 
country  they  may  be  found.  Local  names  have,  after 
this  fashion,  been  given  quite  extensively  by  geologists 
to  different  systems  and  formations,  as  you  will  see  as 
we  proceed.  The  Silurian  system  has  been  very  fully 
examined  in  this  country  in  the  State  of  New  York,  and 
it  is  presented  to  you  in  Fig.  101,  in  a  section  which  was 
drawn  by  Professor  Hall  in  making  his  geological  sur- 
vey. The  section  exhibits  the  arrangement  of  the  sys- 
tem, together  with  the  next  to  be  noticed,  the  Devonian, 
from  the  north  side  of  Lake  Ontario  across  New  York 
into  Pennsylvania.  I  give  below  it  the  names  of  the  dif- 
ferent formations  or  groups  as  they  have  been,  applied 
from  the  local  associations  of  the  rocks. 


Fig.  101. 


1.  A.  Upper  rocks  of  the  Azoic 
age. 

2.  B.  Potsdam   sandstone,  lowest 
of  the  rocks  of  the  Silurian  age. 

3.  C.  Calciferous  sand  rock. 

4.  D.  Black  River  limestone. 

5.  E.  Trenton  limestone. 

6.  F.  Utica  slate. 

a.  Lake  Ontario. 

7.  G.  Hudson  River  group. 


conglomerate. 


9.  I.    Medina  sandstone. 

10.  K.  Clinton  group, 

11.  L/.  Niagara  group. 

12.  m.  Onondaga  salt  group. 

13.  N.  Helderberg  series. 

14.  O.  Hamilton  group. 

15.  e.   Tully  limestone. 

16.  P.  Portage  group. 

17.  R.  Chemung  group. 

18.  S.  Old  red  sandstone. 


8.  H.  Gray  sandstone  and  Oneida  19.  T.  Conglomerate  of  the  Car- 


boniferous system. 


You  see  that  the  rocks  all  crop  out  here,  and  that,  if 
they  laid  horizontally,  as  they  did  when  they  were  depos- 


190  GEOLOGY. 

ited,  the  azoic  rocks,  A,  would  be  underneath  the  whole. 
The  Silurian  system  ends  in  the  Helderberg  series,  and 
the  Devonian  lies  between  this  and  the  beginning  of  the 
Carboniferous  system,  T.  The  old  red  sandstone,  S,  is  so 
prominent  in  the  Devonian  system  in  England  and  Scot- 
land that  its  name  is  there  very  commonly  applied  to  the 
whole  systetn. 

276.  Geographical  Distribution.— The  chief  part  of  the 
rocks  of  this  system  that  come  to  the  surface  in  the 
United  States  lie  along  south  of  the  continent  as  it  was 
begun  in  the  Azoic  age,  as  represented  in  §  267.     They 
are  in  the  great  lake  region,  and  extend  along  in  a  broad 
belt  west  from  Lake  Michigan.     A  long  strip  of  this  sys- 
tem stretches  along  on  the  east  of  the  great  Appalachian 
coal-field,  that  extends  from  Pennsylvania  down  into  Ala- 
bama.    The  Silurian  rocks  are  found  in  the  west  of  En- 
gland, where,  as  I  have  before  said,  they  were  first  suc- 
cessfully examined  ;  also  in  Belgium,  Germany,  Norway, 
Sweden,  and  in  Russia,  in  the  neighborhood  of  St.  Peters- 
burg. 

277.  Copper  of  the  Silurian  Rocks. — In  the  neighbor- 
hood of  Lake  Superior  trap  rocks  were  thrust  upward 
among  the  Silurian  rocks,  and  native  copper  is  found 
there  in  great  abundance  in  veins,  in  both  kinds  of  rocks 
where  they  came  together.     It  is  supposed  that  the  cop- 
per was  produced  from  ores  in  the  azoic  rocks  lying  be- 
low, the  trap,  as  it  came  up  in  its  molten  state,  smelting 
the  ores  as  if  in  a  vast  furnace,  and  forcing  the  pure  metal 
upward,  which,  in  its  melted  state,  passed  into  openings 
and  crevices,  making  veins  in  all  directions. 

278.  Silurian  Salt. — Most  of  the   salt-springs  in  this 
country  issue  from  Silurian  rocks.     The  extensive  accu- 
mulation of  salt  in  the  State  of  New  York  Professor 
Dana  accounts  for  in  the  following  manner.     He  sup- 
poses that  when  the  saliferous  (salt-bearing)  beds  were 
laid  down  there  was  in  that  quarter  a  large  shallow  ba- 
sin, or  series  of  basins,  \\  ith  limestone,  such  as  we  have 


AGE   OP   MOLLUSKS.  191 

at  Niagara  Falls,  for  a  bottom.  Into  these  basins  the 
salt  water  of  the  ocean  was  admitted,  in  some  way,  in- 
termittingly.  This  might  be  from  the  occasional  break- 
ing away  here  and  there  of  the  barriers  which  bounded 
in  these  basins  from  the  sea,  or  simply  from  the  changes 
of  the  tide.  The  result,  you  see,  then,  would  be  some- 
what like  that  which  we  have  in  the  artificial  production 
of  salt  from  evaporation  of  the  waters  of  the  ocean,  as 
noticed  in  §  358,  Part  II.  By  evaporation  over  this  im- 
mense area  of  the  basins  the  salt  of  the  sea-water  would 
be  deposited,  mingled  with  the  mud,  which  would  be  at 
the  same  time  settling  as  sediment.  This  would  go  011 
rapidly  whenever  the  water  was  very  low,  especially 
with  the  warmth  of  climate  which  prevailed  in  that  age. 
And  such  accumulations  of  salt  going  on  for  a  long  pe- 
riod (for  this  salt-making,  like  the  coal-making,  did  oc- 
cupy a  long  time  in  the  world's  geological  history)  would 
lay  up  in  the  rocks  into  which  this  mud  would  change 
by  solidification  a  vast  amount  of  salt,  such  as  we  now 
find  in  the  Silurian  deposits  in  New  York.  Mr.  Dana 
states  that  he  once  saw  in  a  small  coral  island  of  the 
Pacific  a  process  similar  to  this  actually  going  on.  It 
was  an  island  with  a  lagoon  in  it,  having  no  free  com- 
munication with  the  ocean.  The  waters  became  ex- 
tremely salt  in  the  hot,  dry  season,  and  fresh  again  in 
the  rainy  months.  There  was  a  mud  deposited  in  the 
bottom  of  the  lagoon  from  the  wrashing  of  the  coral 
rocks  that  bounded  it.  This  calcareous  mud,  if  solidi- 
fied, would  make  a  saliferous  rock,  like  the  rocks  of  this 
character  in  the  Silurian  system  of  New  York.  The  salt 
is  obtained  from  these  rocks  in  New  York  by  evapora- 
ting the  solution,  or  brine,  made  by  the  water  which 
gains  access  to  the  strata.  At  the  great  salt-works  in 
Salina  and  Syracuse  this  brine  is  collected  by  borings, 
which  sometimes  extend  down  over  300  feet.  From  35 
to  45  gallons  furnish  a  bushel  of  salt,  while  it  requires 
nearly  ten  times  this  quantity  of  sea-water  to  furnish  this 
amount. 


192  GEOLOGY. 

279.  Gypsum.  —  There  is  also  much  gypsum  in  the 
rocks  of  the  saliferous1  epoch  of  the  Silurian  age  in  New 
York.     It  is  found,  not  in  layers,  but  in  masses  imbedded 
in  the  rocks,  from  some  of  which  it  is  supposed  to  have 
been  formed  by  a  chemical  process.     The  explanation  of 
the  process  is  this:  The  sulphureted  hydrogen  issuing 
from  sulphur  springs,  which  abound  in  New  York,  by  be- 
coming oxydized,  produces  sulphuric  acid,  and  this,  act- 
ing upon  the  limestone  (carbonate  of  lime),  unites  with 
the  lime,  driving  off,  of  course,  the  carbonic  acid  (§  60). 
Wherever  gypsum  and  salt  are  found  together,  as  they 
often  have  been,  the  salt,  being  soluble,  may  be  carried 
off  by  water,  if  circumstances  allow  of  drainage,  leaving 
the  insoluble   gypsum  behind.     In  many  cases  where 
gypsum  is  found  alone  there  was  once  salt  in  company 
with  it. 

280.  The  Silurian  Beach. — As  the  land  formed  in  the 
Azoic  age  was  not  elevated  to  any  great  height,  the  land 
which  was  added  to  it  during  the  age  of  Mollusks  was 
mostly  added  as  accumulations  are  now  made  on  a  wide- 
spread beach  by  the  waves  of  the  sea.     So  much  was 
this  the  case,  that  Professor  Agassiz  remarks  that  "  in 
the  Silurian  period,  the  world,  so  far  as  it  was  raised 
above  the  ocean,  was  a  beach."     He  speaks  also  of  cer- 
tain marks  of  water  movements,  usually  seen  on  beaches, 
which  are  now  found  in  the  solid  rocks   of  this  age. 
Even  ripple-marks  made,  not  merely  centuries,  but  thou- 
sands of  centuries  ago,  are  to  be  plainly  seen  now  in  the 
rocky  strata  as  we  divide  the  laminae  and  expose  fresh 
surfaces.     So  there  are  ridges  left  which  are  manifestly 
remains  of  ancient  sea-shores,  formed  one  after  another 
as  the  land,  with  the  accumulation  of  deposits,  encroached 
upon  the  water.     There  are  many  of  these  ridges  to  be 
seen  extending  from  the  neighborhood  of  Lake  Cham- 
plain  toward  the  west,  marking  the  limits  of  the  sea  at 
successive  periods  in  the  age.     They  have  all  the  irreg- 
ularities of  line  and  shape  that  are  witnessed  in  sea- 


AGE    OF    MOLLUSKS.  193 

shores  of  the  present  day.  "  Unstable  as  water"  is  a 
proverb,  the  truth  of  which  has  been  recognized  from 
time  immemorial ;  but  the  water,  though  itself  unstable, 
lias  left  stable  evidences  of  its  work  every  where  in  the 
earth.  It  has  left  traces  in  rock  which  have  lasted  ages 
upon  ages  longer  than  any  chiselings  of  man  upon  mon- 
umental granite. 

281.  Life  in  this  Age. — As  the  beach-arrangement  of 
land  was  prominent,  so,  as  Agassiz  remarks,  the  life  was 
mostly  such  as  we  find  now  on  beaches.     Mollusks  were 
abundant ;  crustaceans  of  some  kinds  also,  and  star-fish- 
es, sea-urchins,  etc.     There  were  corals,  also,  when  and 
where  the  circumstances  were  favorable  to  their  growth. 
I  will  cite  two  instances  in  contrast  in  this  respect.    In 
forming  the  limestone  floor  of  the  great  New  York  ba- 
sins preparatory  to  the  salt-making  (§  278),  the  work 
was  done  by  coral  animal s^  and  other  allied  animals,  as  is 
shown  by  the  abundance  of  their  remains  in  that  rock. 
But  when  the  salt-beds  came  to  be  laid  down  these  ani- 
mals were  absent,  for  the  water  was  too  salt  for  them  to 
live  in,  and  few  fossils  are  therefore  found  in  these  beds. 
The  same  contrast  was  seen  in  the  coral  island  observed 
by  Professor  Dana.     In  the   salt  water   of  the  lagoon 
there  were  no  corals  nor  shells,  though  there  was  a  plen- 
ty of  them  outside  of  the  island  in  the  open  sea.     There 
were  no  insects  in  the  Silurian  age,  and  but  few  fishes ; 
some  think  absolutely  none.     There  were  no  land  nor 
fresh-water  animals.     As  to  vegetation,  we  have  remains 
only  of  the  lowest  forms  of  vegetation,  such  as  sea-weeds 
and  club-mosses.     No  land-plants  have  been  found  ex- 
cept in  the  uppermost  strata.     What  life  there  was  in 
this  age  was  very  abundant  during  most  of  the  period  in 
most  localities.     There  was  such  a  profusion,  says  Agas- 
siz, "  that  it  would  seem  as  if  God,  in  the  joy  of  creation, 
had  compensated  himself  for  a  less  variety  of  forms  in 
the  greater  richness  of  the  early  types." 

282.  Adaptation.— The  life  on  the  earth  at  that  time, 

I 


194  GEOLOGY. 

we  can  see  from  our  reading  of  the  life-record  of  the 
rocks,  was  adapted  to  the  circumstances  of  the  case. 
Though  all  the  four  grand  divisions  of  animals  were  rep- 
resented, there  were  few  vertebrates  or  articulates,  and 
these  were  of  the  lower  orders,  because  the  circumstan- 
ces of  the  world  were  not  suited  to  those  forms  of  life. 
The  animals  were  mostly  marine.  There  were  no  air- 
breathing  animals,  because  the  atmosphere  was  not  in  a 
fit  state  for  them.  There  was  too  much  carbonic  acid  in 
it,  of  which  the  air  was  to  be  relieved  in  after  ages,  as 
will  be  shown  you  in  another  chapter.  There  were  no 
fishes,  partly,  at  least,  because  they  need  dissolved  in  the 
water  which  passes  through  their  gills  air  that  has  a 
good  proportion  of  oxygen  in  it  (Part  II.,  §  93).  In  re- 
gard to  the  adaptation  manifest  in  that  age  of  the  earth, 
Agassiz  very  forcibly  remarks :  "  Let  us  remember,  then, 
that  in  the  Silurian  period,  the  world,  so  far  as  it  was 
raised  above  the  ocean,  was  a  beach,  and  let  us  seek  there 
for  such  creatures  as  God  has  made  to  live  on  sea-shores, 
and  not  belittle  the  creative  work,  or  say  that  he  first 
scattered  the  seeds  of  life  in  meagre  or  stinted  measure, 
because  we  do  not  find  air-breathing  anihials  when  there 
was  no  fitting  atmosphere  to  feed  their  lungs,  insects 
with  no  terrestrial  plants  to  live  upon,  reptiles  without 
marshes,  birds  without  trees,  cattle  without  grass — all 
things,  in  short,  without  the  essential  conditions  for  their 
existence." 

283.  Carbonaceous  Matter  in  Silurian  Shales. — There 
was  no  coal  formed  in  this  age,  for  there  was  no  vegeta- 
ble growth  sufficient  for  this  purpose ;  but  in  the  shales 
there  is  a  considerable  amount  of  carbonaceous  matter 
in  some  localities,  even,  in  some  cases,  up  to  20  per  cent. 
This  came  mostly  from  the  sea-weeds,  which,  gathering 
the  carbonic  acid  from  the  air,  appropriated  to  their  own 
growth  the  carbon,  and  gave  the  oxygen  to  the  animals 
of  the  sea  (Part  II.,  §  95). 

284.  Hydrozoa  and  Bryozoa. — In  Fig.  102  we  have  the 


AGE  OF    MOLLUSKS. 


195 


1.  Oldhamia.     2.  Protovirgularia.     3.  Graptolites.     4,5.  Diplograpsus.     6.  Did- 
ymograpsus.    7.  Rastrites. 

Fig.  102. 

frame-works  of  certain  small  animals  called  Hydrozoa 
and  Bryozoa,  some  of  which  contributed  much  to  the 
material  for  the  formation  of  rocks  in  the  Silurian  age. 

285.  Corals  and  Echinoderms. — In  Fig.  103  we  have 
specimens  of  these  two  divisions  of  the  Radiates,  which 


1.  Heliolites. 
6.  Palseaster. 


2.  Catenipora.    3.  Cyathophyllum.    4.  Taxocrinus.     5.  Cystid 
Fig.  103. 

had  so  much  to  do  with  supplying  the  material  for  the 
limestones  in  the  age  of  Mollusks.     One  of  the  most 


196 


GEOLOGY. 


beautiful  of  the  corals  is  given  in  Fig.  104,  the  chain  cor- 
al, the  specimen  pictured  being  from  the  cliff  limestone 


Fig.  104. 

in  Iowa.  The  Echinoderms  styled  crinoids,  of  which  4 
and  5,  Fig.  103,  are  specimens,  stand 
on  stems  or  peduncles.  In  Fig.  105 
is  represented  the  base  of  the  frame- 
work of  one  of  these  animals.  To 
the  central  piece  was  fastened  the 
peduncle,  and  the  branching  arms 
of  the  animal  were  jointed  to  the 
side  pieces.  The  fragments  of  the 
stems  of  these  animals  found  in  the 

rocks  were  used  as  rosaries  in  the  Middle  Ages.     They 

were  called  St.  Cuthbert's  beads,  and  are  thus  noticed  by 

Sir  Walter  Scott  in  his  Marmion  : 

"  On  a  rock  by  Lindisfarn 
St.  Cuthbert  sits,  and  tries  to  frame 
The  sea-born  beads  that  bear  his  name." 

286:  Mollusks. — In  Fig.  106  you  have  specimens  of  the 
shells  of  some  of  the  varieties  of  Silurian  mollusks.  There 
are  three  great  classes  of  mollusks.  1.  The  Cephalopoda, 


Fig.  105. 


AGE    OF   MOLLUSKS. 


197 


1.  Lingula.     2.  Rhynconella.     3.  Pentamerus.    4.  Strophomena.     5.  Spirifer. 
6.  Murchisonia.     7.  Orthoceras.     8.  Lituites.     9.  Maclurea. 
Fig.  106. 

which  have  arms  or  feet  about  the  mouth,  the  name  com- 
ing from  the  Greek  works  Tcephale,  head,  and  pous,  foot. 
The  shells  of  this  class  are  more  often  curved  on  one 
plane,  as  8,  than  spiral,  as  6.  In  8  we  have  a  chambered 
shell — an  arrangement  that  is  found  in  almost  all  of  this 
class — the  cavity  being  divided  by  partitions  into  cham- 
bers, which  have  a  tube,  called  the  siphuncle,  running 
through  them.  The  use  of  this  is  explained  in  my  Nat- 
ural History,  §  554.  2.  G-asteropods.  The  name  of  this 
class  comes  from  gaster,  belly,  audpous.  These  mollusks 
creep  on  a  broad  disk  or  foot,  as  you  see  represented  in 
Fig.  107  (p.  198).  The  head  and  the  broad  foot,  which 
are  out  of  the  shell  as  the  animal  crawls  along,  can  be 
withdrawn  within  the  shell.  The  common  snail  is  an 
example  of  this  class.  3.  The  Acephals.  These  have  no 
heads,  as  the  name  indicates,  the  a  being  the  a  privative 
of  the  Greek.  Of  these  there  are  two  divisions — the  com- 
mon bivalves,  as  oysters  and  clams,  which  have  two  equal 
valves,  and  those  which  have  two  unequal  valves.  These 


198  GEOLOGY. 


Fig.  107. 

latter  have  also  peculiar  arms,  from  which  they  are  com- 
monly called  JBrachiopods,  from  brachion,  arm,  audpous. 
The  valves  are  symmetrical,  as  seen  in  1,  2,  3,  4,  and  5, 
Fig.  106,  which  are  all  Brachiopods.  The  Brachiopods 
were  much  more  abundant  in  the  Silurian  age  than  the 
common  bivalves,  but  the  reverse  is  the  case  at  the  pres- 
ent time.  The  small  shell,  Lingula,  1,  is  some- 
times found  in  rocks  in  such  abundance  as  to 
.give  them  their  name,  as  Lingula  flags  and  Lin- 
gula grits.  The  Orthoceras,  7,  is  a  chambered 
shell,  like  the  pearly  Nautilus  of  our  day,  or  the 
Lituites  in  the  figure,  but  as  if  unrolled,  so  as  to 
be  straight.  Some  specimens  are  ten  or  fifteen 
feet  in  length  and  a  foot  in  diameter.  These 
were  the  monster  mollusks  of  the  Molluscan 
age.  In  Fig.  108  is  represented  the  internal 
arrangement  of  the  shells  of  these  Orthocera- 
tites.  The  Cephalopods,  with  their  chambered 
cells,  were  very  numerous  in  the  Silurian  and 
°^er  aneient  ages,  but  at  the  present  time  there 
are  about  half  a  dozen  living  species,  and  these 
belong  to  the  genus  Nautilus.  In  Fig.  109  we  have  a 
representation  of  a  remarkable  shell  of  a  cephalopod  from 
the  Silurian  rocks  of  Russia. 

287.  Trilobites. — The  family  of  Trilobites,  of  which 
there  is  not  a  species  now  in  existence,  furnished  the 


AGE    OF    MOLL 


Fig.  109. 


chief  representatives  of  the  division  of  Articulates  called 
Crustaceans  in  the  age  of  Mollusks.  Some  of  the  species 
of  this  extensive  family  are  shown  in  Fig.  110.  These 


1.  Phacops.    2.  Trinucleus.    3.  Ampyx.    4.  Ogygia.    5.  Ilsenns.     6.  Calymene. 
7.  Calymene  coiled  up. 

Fig.  110. 

animals,  as  you  see,  are  divided  lengthwise  into  three 
lobes,  and  hence  comes  their  name.  They  have,  trans- 
verse to  these,  the  common  ring-like  divisions  of  the  Ar- 
ticulates. Their  eyes,  which  were  quite  prominent,  were 
compound.  They  had  the  power  of  curling  themselves 
up  like  the  wood-louse,  as  exhibited  in  Fig.  Ill  (p.  200). 


200  GEOLOGY. 

In  Fig.  110,  1  is  the  same  with 
6,  but  represented  as  coiled  up. 
The  fossils  of  these  animals  are 
often  found  in  this  posture  in  the 
rocks,  showing  that  the  envelop- 
ing mud  or  sand,  which  after- 
ward became  stone,  caught  them 
in  this  condition.  The  size  of 
Fig.  111.  these  animals  varied  much,  from 

the  sixth  of  an  inch  to  even  two  feet  in  length. 

288.  Climate. — The  climate  of  the  Silurian  age,  it  is 
supposed,  was  quite  uniformly  warm  over  the  whole 
earth.     Mollusks  are  not  apt  to  be  profusely  abundant 
except  in  warm  seas,  but,  as  the  life-record  shows  that 
they  Avere  so  in  such  localities  as  New  York,  it  is  plain 
that  tropical  climes  were  more  extensive  than  now.     Be- 
sides, the  wide  diffusion  of  the  mollusks  shows  that  the 
temperature  of  the  earth  generally  was  more  equal.    That 
the  sun  shone  then  with  clearness  much  of  the  time,  how- 
ever it  might  have  been  in  the  Azoic  age  (§  271),  is  plain 
from  the  eyes  which  the  Creator  gave  to  those  numerous 
inhabitants  of  the  sea,  the  Trilobites. 

289.  Alternate  Subsidences  and  Elevations. — During 
the  different  periods  of  this  age  there  must  have  been 
many  changes  in  the  level  of  the  land  when  different 
strata  were  forming.     Take  a  single  example.     When 
the  great  limestone  floor  of  the  New  York  basins  (§278) 
was  being  laid,  the  water  must  have  been  of  the  requi- 
site depth  for  the  corals,  and  crinoids,  and  mollusks  that 
flourished  then.     For  this  purpose  there  was  a  subsi- 
dence of  the  land,  and  there  is  evidence  that  this  move- 
ment extended  far  beyond  the  locality  of  these  basins. 
For  instance,  the  Green  Mountain  region,  which  had  pre- 
viously been  dry  land,  was  now  wholly  or  in  part  sub- 
merged.    But  when,  after  the  floor  was  laid,  the  salty 
deposits  were  made,  there  was  an  elevation  of  the  land 
that  shallow  waters  might  prevail  for  the  ready  evapora- 
tion of  the  water  and  the  consequent  deposit  of  the  salt. 


AGE    OF    FISHES.  201 


CHAPTER  XV. 

AGE   OF   FISHES,  OE   DEVONIAN   AGE. 

290.  Rocks. — The  rocks  formed  in  this  age  are,  in 
North  America,  in  the  first  part  of  the  age,  limestones, 
and  afterward  mostly  sandstones,  shales,  and  flags.     The 
famous  North  River  flagging-stones  were  made  in  this 
age.     So  also  were  the  Scotch  flagging-stones  known 
over  Europe  as  the  Caithness  flags  of  commerce.     The 
Devonian  system  of  England  and  Scotland  has  the  gen- 
eral name  of  Old  Red  Sandstone,  red  sandstone  being 
there  the  principal  rock  of  the  system.     The  name  De- 
vonian was  given  to  this  system  because  its  rocks  were 
early  investigated  by  Murchison  in  Devonshire,  England. 

291.  Extent  of  the  System  in  this  Country. — The  De- 
vonian rocks  cover  a  large  area  in  the  interior  of  this 
country,  extending  along  south  of  the  addition  which 
was  made  in  the  age  of  Mollusks  to  the  continent  as  it 
was  begun  in  the  Azoic  age.     Lake  Erie  is  included  in 
this  space.     Lake  Michigan  bounds  it  on  the  west,  and 
a  long,  narrow  arm  of  it  extends  from  a  little  below  this 
lake  far  to  the  northwest.     This  area  extends  broadly 
down  the  west  side  of  the  Appalachian  coal  formation 
two  thirds  of  its  length,  tapering,  however,  as  it  goes. 
This  immense  Devonian  field  has  a  broad  eastern  branch 
extending  from  Lake  Erie  to  within  a  short  distance  of 
the  Hudson  River.     It  is  this  part  of  the  field,  reaching 
down  into  Pennsylvania,  which  is  represented  in  the  sec- 
tion given  in  Fig.  101,  beginning  in  N,  the  Helderberg 
series,  and  ending  in  S,  the  Old  Red  Sandstone.     Perhaps 
some  of  this  large  extent  of  territory  has  had  some  of 
the  Devonian  strata  covered  by  other  rocks  of  a  later 

12 


202  \         GEOLOGY. 

formation,  but,  if  so,  they  have  been  denuded  by  the  ac- 
tion of  water. 

292.  Devonian  System  in  Europe. — Devonian  rocks  are 
found  in  most  of  the  countries  of  Europe.     In  Germany 
they  cover  a  larger  space  than  the  Silurian.     This  sys- 
tem is  very  marked  in  England,  and  also  in  Scotland, 
where  the  genius  of  the  lamented  Hugh  Miller  has  given 
it  a  deep  but  melancholy  interest.     In  Russia,  south  of 
St.  Petersburg,  it  covers  an  area  of  150,000  square  miles. 
In  connection  with  the  Devonian  of  Russia,  I  will  men- 
tion an  interesting  example  of  geological  investigation. 
It  was  doubted  for  some  time  whether  the  red  sand- 
stone of  Devonshire  was  of  the  same  period  with  that 
of  Hereford,  because  the  strata  of  Devon  contained  cer- 
tain shells  which  were  not  found  in  the  rocks  of  Here- 
ford, while  the  latter  contained  fishes  that  were  not  found 
in  those  of  Devon.     Sir  R.  Murchison  settled  this  ques- 
tion by  finding  in  Russian  strata  both  the  shells  of  De- 
von and  the  fishes  of  Hereford.   You  see  what  this  shows 
— that  the  rocks  in  Russia,  in  Devon,  and  in  Hereford 
belong  to  the  same  epoch,  and  that  the  fact  that  the 
fishes  and  shells  were  not  found  together  in  both  Devon 
and  Hereford  was  owing  to  some  local  causes. 

293.  Coral  Formations. — I  have  stated  in  §  290  that 
the  strata  of  this  age  first  laid  down  were  limestones. 
The  corals  had  a  great  agency  in  providing  material  for 
these.     Indeed,  the  upper  Helderberg  period  was,  Pro- 
fessor Dana  states,  "  eminently  the  coral-reef  period  of 
the  Palaeozoic  ages."     Near  Louisville,  Kentucky,  at  the 
Falls  of  the  Ohio,  there  is  a  grand  display  of  the  lime- 
stone of  this  period,  very  much  like  a  coral  reef  of  the 
present  time.     At  all  seasons  when  the  water  is  not  high 
a  series  of  ledges  is  exposed,  and  the  softer  parts  of  the 
rock  having  been  worn  away,  the  harder  corals  stand  out 
in  bold  relief,  and  many  of  them  branch  out  precisely  as 
if  they  were  living.     There  are  honey-comb,  cup-shaped, 
star-like,  and  other  forms  mingled  with  the  joints,  stems, 


AGE   OF    FISHES.  203 

and  heads  of  criooids.     Among  them  is  seen  a  species 
of  the  family  Favosites,  having  a  beautiful  honey-comb 
structure,    and    appearing    in 
masses  in   some   cases   of  not 
less  than  five  feet  in  diameter. 
A  species  of  this  family  is  rep- 
resented in  Fig.  112.     The  ele- 
Fig.ii2.  gant  cbain  cora]}  Fig.  104,  is 

also  present  in  this  locality. 

294.  Variety  in  Rock-making  at  the  same  Period. — 
Different  kinds  of  rock-making  were  sometimes  going  on 
at  the  same  time  over  different  parts  of  the  Devonian 
area  itf'  this  country,  and  the  same  is  true  of  other  coun- 
tries also.     Thus,  at  one  period,  while  corals,*  crinoids, 
etc.,  were  accumulating  limestones  over  a  large  area  in 
the  Western  States,  over  New  York  there  were  exten- 
sive flats  forming  and  solidifying  into  sandstones,  and 
shales,  and   flags.     Here   are  found  ripple-marks   and 
shrinkage  cracks,  showing  that  the  flats  were  sometimes 
covered  with  shallow  water,  and  sometimes  drying  in 
the  sun.     The  ripple-marks  in  the  flags  are  so  even  and 
extensive  that  it  is  obvious  that  the  sea  swept  over  wide- 
spread flats.     While  this  was  going  on  in  New  York, 
there  was  at  the  West,  where  the  corals  and  crinoids 
were  building  limestone,  an  interior  sea  of  vast  extent, 
and  of  suitable  depth  for  these  animals  to  flourish  in. 

295.  Devonian  Vegetation. — In  the  age  of  Fishes  there 
was  not  only  more  marine  vegetation  than  in  the  age  of 
Mollusks,  but  land  vegetation  appeared,  and  before  the 
middle  of  the  age  had  passed  it  had  covered  the  com- 
paratively small  portions  of  the  continents  that  had  fairly 
risen  above  the  ocean  and  remained  so.     At  the  close  of 
the  age  the  State  of  New  York,  although  it  had  been 
previously  submerged,  formed  a  part  of  the  land  which 
was  thus  covered.     The  plants,  as  we  approach  the  con- 
clusion of  this  age,  become  more  and  more  like  those  of 
the  next  age,  thus  exemplifying  that  foreshadowing  of 


204  GEOLOGY. 

which  I  have  spoken  in  §  262.  Indeed,  there  has  actu- 
ally been  found  some  coal  in  some  of  the  rocks,  in  addi- 
tion to  the  carbonaceous  shales,  which  appear  now  as 
they  did  in  the  Silurian  system. 

296.  Animal  Life. — As  there  was  a  considerable  ad- 
vance upon  the  previous  age  in  the  forms  of  vegetable 
life,  there  was  a  corresponding  one  in  those  of  animal 
life.     Few,  if  any,  vertebrates  existed  in  the  Silurian  age, 
but  now  they  abounded  in  the  form  of  fishes.     Some  rep- 
tiles also  appeared,  though  not  in  much  variety.     There 
is  no  evidence  of  the  existence  of  any  insects,  or  birds, 
or  mammals. 

297.  Mollusks. — Of  the  Mollusks  there  was  a^  abun- 
dant a  variety  of  species  as  in 

the  previous  age.     Of  the  Bra- 


Fig.  113. 

chiopods,  the  genus  Stri- 
gocephalus,  of  which  Fig. 
113  represents  one  spe- 
cies, was  introduced  at 
this  period.  Of  the  Ce- 
phalopods,  the  genus  Cly- 
menia  was  introduced,  of 
which  Fig.  114  represents 
one  species.  Thirty- five 
species,  which  is  nearly 

all  under  this  genus,  have  been  found  in  the  rocks  of  one 
locality  in  Bavaria. 

298.  Crustaceans. — The  Trilobites,  whose  species  were 
numbered  by  the  hundreds  in  the  Silurian  age,  now 
amounted  to  a  dozen  or  two.  But  there  are  some  very 
extraordinary  Crustaceans,  which,  beginning  to  appear 
in  the  age  of  Mollusks,  were  now  very  abundant.  They 


AGE    OF   FISHES. 


205 


were  singular  in  their  formation,  combining  in  one  ani- 
mal the  qualities  of  various  kinds  of  animals.  "  King- 
crab-like,"  says-  Page,  "  in  their  carapace  and  organs  of 
mastication,  lobster-like  in  their  prolonged  and  segment- 
ed bodies,  furnished  with  broad,  paddle-like  swimming 
limbs,  and  frequently  with  huge  prehensile  claws,  they 
present  the  zoologist  with  an  entirely  distinct  family,  if 
not  with  the  elements  of  a  new  and  separate  legion. 
Some  of  the  species  are  of  great  size — three,  four,  and 
six  feet  in  length — and  seem  to  have  been  the  scaven- 
gers of  their  period,  living  on  the  lower  forms  and  garb- 
age of  the  sea-shore."  One  of  these  is  pictured  in  Fig. 
115,  lying  on  his  back.  In  the  same  rocks  in  which  are 


Fig.  115. 

the  remains  of  these  Crustaceans  there  are  found  patches 
of  spawn-like  appearance,  which,  though  they  have  been 
supposed  by  some  to  be  berries  of  some  plant,  are  now 
generally  regarded  as  the  egg-packets  of  these  animals. 
The  eggs  are  flattened,  and  they  have  more  or  less  of  a 
concentric  arrangement,  as  seen  in  Fig.  116  (p.  206). 

299.  Fishes. — That  you  may  understand  the  record 
which  these  animals  have  made  of  themselves  in  the 
rocks  of  this  and  other  ages  also,  I  will  here  notice  the 


206  GEOLOGY. 


Fig.  116. 

classification  of  fishes.  Agassiz  discovered  that  there  is 
such  a  relation  between  the  form  of  the  scale  and  the  in- 
ternal organization  of  the  fish,  that  those  which  have  sim- 
ilar scales  are  similar  in  their  general  character.  This 
discovery  is  of  great  importance  in  studying  the  palaeon- 
tology of  fishes,  because  the  scales  are  so  often  preserved 
in  the  rocks  when  the  other  structures  of  fishes  have  per- 
ished. It  is  on  this  account  that  while  the  classification 
of  Cuvier  answers  admirably  for  living  forms,  that  of 
Agassiz  is  altogether  better  for  the  fossils.  The  four  or- 
ders of  Agassiz  are  as  follows:  1.  Placoids.  The  name 
comes  from  a  Greek  word?jpte,  a  broad  plate.  The  skin 
in  this  order  is  covered  with  broad,  irregular  plates  of 
enamel,  as  in  the  shark  family.  The  skeleton  is  soft  and 
cartilaginous,  much  of  the  firmness  of  the  animal  depend- 
ing upon  the  external  covering,  which  may  be  considered 
in  part  as  an  external  skeleton.  In  Fig.  117, 1,  is  repre- 
sented one  of  the  plates,  and  at  2  one  of  the  prickly  tu- 
bercles of  the  ray-fishes,  which  belong  to  the  same  order. 
2.  Ganoid.  This  term  comes  from  ganos,  splendor. 
Fishes  of  this  order  are  covered  in  a  regular  manner 
with  scales  of  horn  or  bone,  having  a  thick  outer  layer 
of  enamel,  which  is  hard  and  bright.  Such  a  scale  is  fig- 
ured at  3.  The  sturgeon  and  trunk-fish  belong  to  this 
order.  3.  Ctenoid.  This  name,  from  kteis,  a  comb,  in- 
dicates scales,  4  and  5,  which  are  toothed  or  jagged  on 
the  posterior  margin.  The  perch  is  an  example  of  this 
order.  4.  Cycloid.  The  term  comes  from  kufdos,  a  cir- 


207 


Fig.  117. 

cle.  The  scales,  6,  have  a  simple  and  smooth  margin, 
and  their  outer  surface  is  often  variously  ornamented. 
In  this  order  are  the  salmon,  the  carp,  and  the  pike. 

I  shall  have  occasion  to  refer  to  these  orders  hereaf- 
ter. Suffice  it  to  say  now  that  the  placoids  and  ganoids 
had  their  greatest  developments  in  the  Palaeozoic  ages, 
and  that  there  are  few  of  them  at  the  present  time,  while 
the  ctenoids  and  cycloids  came  on  at  a  later  age,  and 
abound  in  the  waters  of  the  present  period.  Four  fifths 
of  the  present  fishes  belong  to  the  ctenoid  and  cycloid 
orders,  the  remaining  fifth  consisting  of  placoids,  with  a 
small  number  of  ganoids. 

300.  Coccosteus,  Pterichthys,  and  Cephalaspis.  —  The 
fishes  of  the  Devonian  age  whose  names  I  have  here 
given  are  ganoids,  having  very  peculiar  characteristics. 
The  Coccosteus,  or  "berry-bone,"  1,  Fig.  118  (p.  208),  has 
the  largest  part  of  the  body  incased  in  a  box-like  cover- 
ing of  bony  plates,  upon  which  there  are  berry-like  projec- 
tions. The  Pterichthys,  or  "  wing-fish,"  2,  which  Hugh 
Miller,  its  discoverer,  termed  the  characteristic  organism 
of  the  old  red  sandstone,  is  so  extraordinary  that  Agassiz 
says  of  it  that "  it  is  impossible  to  find  any  thing  more 
eccentric  in  the  whole  creation."  On  the  head  was  a 


208 


GEOLOGY. 


Fig.  118 


strong  helmet  with  two  circular  holes  in  front  for  the 
eyes.  The  chest  and  back  were  covered  by  a  curiously- 
constructed  cuirass  formed  of  plates,  and  the  tail  was 
sheathed  in  a  flexible  mail  of  bony  scales.  The  arms  are 
also  covered  with  plates.  There  are  peculiarities  in  the 
jointing  of  the  different  parts  of  this  bony  covering,  and 
in  the  contrivances  for  securing  lightness  with  strength, 
which  are  very  curious.  Hugh  Miller  says  of  it  that, 
"  with  its  inflexible  cuirass  and  its  flexible  tail,  and  with 
its  two  arms,  that  combined  the  broad  blade  of  the  pad- 
dle with  the  sharp  point  of  the  spear,  it  might  be  regard- 
ed, when  in  motion,  as  a  little  subaqueous  boat  mounted 
on  two  oars  and  a  scull."  He  farther  says  that  "  when, 
in  laying  open  the  rock  in  which  it  lies,  the  under  part  is 
presented,  as  usually  happens,  we  are  struck  with  its  re- 
semblance to  a  human  figure,  with  the  arms  expanded, 
as  in  the  act  of  swimming,  and  the  legs  transformed^  as 
in  the  ordinary  figures  of  the  mermaid,  into  a  tapering 
tail."  The  correctness  of  this  description  can  be  seen  in 
Fig.  119.  The  Cephalaspis,  or  "buckler-head,"  3,  Fig. 
118,  is  so  called  from  the  shield-like  shape  of  the  bony 
head-plate,  which  is  all  in  one  piece. 


AGE    OF    FISHES. 


209 


Fig.  119. 

301.  Asterolepis. — This  is  another  of  the  ganoids  of 
the  Old  Red  Sandstone.  It  equaled  in  size  the  largest  of 
alligators.  The  helmet  on  its  head  was  made  of  strong 
bony  plates,  ornamented  with  star-like  markings,  and  its 
body  was  covered  with  a  mail  of  scales  which  looked  as 
if  they  had  been  carved  in  the  most  delicate  manner.  It 
is  stated  by  Hugh  Miller  that  helmets  of  this  creature 
"  have  been  found  in  the  flag-stones  of  Caithness  large 
enough  to  cover  the  front  skull  of  an  elephant,  and  strong 
enough  to  have  sent  back  a  musket  bullet  as  if  from  a 
stone  wall."  But  what  was  most  strange  of  all  is  that, 
although  the  Asterolepis  was  a  fish,  it  had  in  the  arrange- 
ments of  its  jaws  and  teeth  the  complete  characteristics 
of  a  reptile.  Here  is  an  example,  in  another  form,  of  the 
foreshadowing  spoken  of  in  §  262.  We  see,  in  this  age 
of  Fishes,  stamped  unmistakably  upon  some  of  these  an- 


210  GEOLOGY. 

imals  characteristics  of  the  reptiles  which  are  to  abound 
so  largely  in  one  of  the  following  ages  as  to  give  it  its 
name.  When  such  mingling  of  the  characteristics  of  two 
or  more  classes  of  animals  occurs  in  one  animal,  it  is  said 
to  be  a  comprehensive  type.  Such  types  were  quite  com- 
mon in  the  forming  ages  of  the  world,  but  as  it  advanced 
to  its  fully-developed  condition,  in  preparation  for  the  ad- 
vent of  man,  the  classes  of  animals  became  more  distinct- 
ly defined,  and  at  the  present  time  such  comprehensive 
types  are  rare  exceptions — so  rare  as  to  be  regarded  .as 
great  curiosities  in  nature.  One  of  these  is  the  duck- 
billed Platypus  of  Australia,  noticed  in  §  133  in  my  Nat- 
ural History. 

302.  Tails  of  the  Ancient  Fishes —Nearly* all  the  fishes 

whose  remains  are  found 
in  the  earlier  strata  of  the 
earth's  rocks  had  unilobed 
tails,  as  seen  in  Fig.  120 — 
that  is,  the  spinal  column 
Fis- 12°-  ran  into  the  upper  lobe  of 

the  tail,  the  lower  being  so  small 

as  not  to  be  counted  as  a  lobe. 

In  the  later  strata,  on  the  oth- 
er hand,  the  tails  are  bilobed, 

Fig.  121,  in  the  great  majority 

of  the  fossils.    At  the  present 

time  the  only  family  of  fishes   *  Fig.  121. 

that  has  the  unilobed  tails  is  the  Shark  family. 

303.  Abundance  of  Devonian  Pishes. — In  estimating 
the  abundance  of  ancient  fishes  from  their  fossils,  we  are 
to  consider  how  uncommon  a  thing  it  must  be  for  fishes 
to  become  enveloped  in  sand  or  mud,  in  comparison,  for 
example,  with  shells.     Keeping  this  in  view,  the  great 
number  of  species  that  have  been  made  out  from  the  fos- 
sils in  some  quarters,  especially  in  Great  Britain  and  Eu- 
rope, indicates  that  fishes  must  have  been  very  abundant 
in  the  Devonian  age.     In  some  cases  great  numbers  must, 


AGE    OF   FISHES.  211 

from  some  cause,  have  been  suddenly  destroyed  and  bur- 
ied at  the  same  time,  for  Hugh  Miller  states  that  there 
are  strata  in  Scotland  where  they  lie  as  thickly  as  her- 
rings do  on  the  fishing-banks  in  the  time  of  the  fisher- 
man's harvest.  And  often  there  is  positive  proof  of  their 
having  been  suddenly  killed  and  buried  in  their  contorted 
attitudes.  Undoubtedly,  in  such  cases,  the  fishes  were 
overwhelmed  with  the  material  in  which  they  were  en- 
veloped by  some  great  convulsion,  and  then  they  became 
fossilized  in  the  rock  into  which  this  material  was  con- 
verted by  solidification. 

304.  United  States  at  the  End  of  this  Age. — I  have 
given  you  in  §  267  some  idea  of  the  beginning  of  the 
continent  of  North  America  in  the  Azoic  age,  and  in 
§276  some  idea  of  the  additions  which  were  made  in 
the  Silurian  age.  During  the  Devonian  age  additions 
were  made  on  the  south  and  southwest,  carrying  out  the 
plan  already  begun,  as  indicated  in  Fig.  100.  Agassiz 
has  stated  what  these  additions  were.  He  says  that  so 
much  was  added  that  at  the  conclusion  of  the  age  there 
were  above  the  water  within  the  United  States  "the 
greater  part  of  New  England,  the  whole  of  New  York, 
a  narrow  strip  along  the  north  of  Ohio,  a  great  part  of 
Indiana  and  Illinois,  and  nearly  the  whole  of  Michigan 
and  Wisconsin."  Besides  this,  from  upheavals  at  the 
close  of  this  period,  there  were,  in  place  of  the  Rocky 
Mountains  at  the  West,  and  of  the  Appalachian  chain, 
which  now  stretches  as  a  rocky  wall  from  New  England 
to  Alabama,  detached  islands  and  reefs  amid  shallow 
waters.  One  of  the  upheavals  that  occurred  at  the  con- 
clusion of  the  Devonian  age  raised  the  high  ground  on 
which  the  city  of  Cincinnati  now  stands.  Of  this  hill 
Agassiz  says,  "  The  granite  did  not  break  through, 
though  the  force  of  the  upheaval  was  such  as  to  rend 
asunder  the  Devonian  deposits,  for  we  find  them  lying 
torn  and  broken  about  the  base  of  the  hill ;  while  the  Si- 
lurian beds,  which  should  underlie  them  in  their  natural 


212  GEOLOGY. 

position,  from  its  centre  and  summit.  This  accounts  for 
the  great  profusion  of  Silurian  organic  remains  in  that 
neighborhood.  Indeed,  there  is  no  locality  which  forces 
upon  the  observer  more  strongly  the  profusion  and  rich- 
ness of  the  early  creation,  for  one  may  actually  collect 
the  remains  of  Silurian  shells  and  Crustacea  by  cart-loads 
around  the  city  of  Cincinnati.  A  naturalist  would  find 
it  difficult  to  gather  along  any  modern  sea-shore,  even 
on  tropical  coasts,  where  marine  life  is  more  abundant 
than  elsewhere,  so  rich  a  harvest,  in  the  same  time,  as  he 
will  bring  home  from  an  hour's  ramble  in  the  environs 
of  that  city." 

305.  Scenery  of  this  Age. — During  most  of  the  Devo- 
nian age  the  scenery  must  have  been  exceedingly  tame 
and  monotonous.  "  Over  dark  and  shallow  seas,"  says 
Hugh  Miller,  "  mud-banks  of  vast  extent  occasionally 
raised  their  flat,  dingy  backs,  and  remained  hardening  in 
the  hot  sun  until  their  oozy  surfaces  had  cracked  and 
warped,  and  become  hard  as  the  sun-baked  brick  of 
Eastern  countries  ;  and  then,  ere  the  seeds  of  terrestrial 
plants,  floated  from  some  distant  island,  or  wafted  in  the 
air,  had  found  time  to  strike  root  into  the  crevices  of  the 
soil,  some  of  the  frequent  earth-tremors  of  the  age  shook 
the  flat  expanse  under  the  water  out  of  which  it  had 
arisen,  and  the  waves  rippled  over  it  as  before."  And 
when  vegetation  obtained  any  where  a  foothold  upon  the 
land,  as  was  the  case  quite  extensively  in  the  latter  part 
of  the  age  (§  295),  it  was  comparatively  scanty,  and 
there  was  none  of  that  variety  of  surface  which  we  have 
now,  for  there  were  no  lofty  mountains  nor  large  rivers. 
Besides,  there  were  no  birds  nor  four-footed  beasts  to 
enliven  the  scene. 


AGE   OF   COAL.  213 


CHAPTER   XVI. 

THE  CARBONIFEROUS    AGE,  OR   AGE   OF   COAL. 

306.  Propriety  of  the  Name. — Nothing  has  been  made 
more  plain  by  the  investigations  of  geologists  than  that 
thousands  of  centuries  ago  there  was  an  age,  and  that  a 
very  long  one,  devoted  expressly  by  the  Creator  to  the 
formation  and  storing  up  of  coal  for  the  future  use  of 
man.     It  seems  eminently  proper,  therefore,  to  call  this 
the  Age  of  Coal,  or  the  Carboniferous  Age.     Observe 
that  all  the  other  ages  that  transpired  during  the  forma- 
tion of  the  earth  were  marked  by  the  predominance  of 
certain  classes  of  animals,  and  are  named  accordingly; 
but  this  is  named  from  a  mineral  production  which  came, 
as  you  have  seen  in  §  42,  from  certain  chemical  changes 
in  vegetable  substances.     Animals  of  most  of  the  various 
classes  were  abundant  in  this  age,  but  no  class  was  espe- 
cially predominant  over  all  the  others,  so  that  it  is  im- 
possible to  derive   a  name  from  that  source.     There 
seems  to  be  no  room  for  choice,  then,  but  we  are  driven 
to  the  name  which  has  been  adopted  by  universal  con- 
sent. 

307.  Localities  of  Coal. — There  are  more  and  larger 
beds  of  coal  in  North  America  than  in  any  other  part  of 
the  world.     Great  Britain  comes  next  in  order.     The 
coal  there  is  mostly  bituminous,  more  or  less,  while  in 
this  country  there  are  large  quantities  of  the  anthracite, 
or  non-bituminous  coal.     Pennsylvania  has  a  larger  area 
of  coal  in  proportion  to  its  whole  area  than  any  other 
part  of  the  world.     There  is  coal  in  Spain,  France,  Bel- 
gium, and  Germany.     Russia  exhibits  over  a  wide  area 
some  of  the  rocks  of  the  coal  period,  but  has  very  little 
coal. 


214  GEOLOGY. 

308.  Amount  of  Coal. — The  amount  of  coal  in  the  prin- 
cipal coal-fields  in  the  world  has  been  estimated  by  Pro- 
fessor H.  D.  Rogers  as  follows : 

Belgium 36,000,000,000  tons. 

France 59,000,000,000 

British  Isles 190,000,000,000 

Pennsylvania 316,000,000,000 

Appalachian  coal-field 1,387,000,000,000 

Indiana,  Illinois,  and  Kentucky 1,277,000,000,000 

Iowa,  Missouri,  and  Arkansas 739,000, 000, 000 

Total  amount  in  North  America.... 4, 000, 000, 000,000 
The  anthracite  of  this  country  was  first  introduced  into 
use  in  blacksmithing  by  Judge  Obadiah  Gore,  a  Con- 
necticut blacksmith,  in  Wilkesbarre,  a  few  years  less  than 
a  century  ago;  but  it  did  not  come  into  common  use 
until  between  thirty  and  forty  years  since.  In  1820  the 
amount  worked  in  Pennsylvania  was  only  380  tons.  Its 
use,  however,  from  that  time  increased  rapidly,  and  in 
1847  that  state  furnished  over  three  million  of  tons,  be- 
sides two  million  of  bituminous  coal.  The  United  States 
produced  in  1857  ten  and  a  half  million  of  tons  ;  and  if 
our  annual  consumption  should  be  twelve  million  of  tons, 
it  is  calculated  that  there  is  coal  enough  in  North  Amer- 
ica to  last  us  333,333  years. 

309.  Extent  of  Coal-fields. — Coal-fields  vary  much  in 
extent,  the  largest  in  the  world  being  in  North  America. 
The  most  extensive  of  all  is  the  Appalachian.     This  oc- 
cupies parts   of  Pennsylvania,  Ohio,  and  Virginia,  the 
eastern  portion  of  Kentucky  and  Tennessee,  and  extends 
down  into  Alabama.     It  covers  an  area  of  80,000  square 
miles,  60,000  of  this  being  available.     This  is  about  ten 
times  as  great  a  space  as  that  occupied  by  all  the  pro- 
ductive coal-fields  of  Great  Britain.     Then  there  is  the 
Indiana,  Illinois,  and  Kentucky  coal-field,  covering  a 
space  of  50,000  square  miles,  and  the  Iowa  and  Mis-souri 
coal-field,  60,000.     The  New  England  coal-field  occupies 
an  area  of  only  about  600  square  miles. 

310.  Arrangement  of  the  Coal-strata. — The  coal  is  in 


AQE    OF    COAL.  215 

strata  or  seams  of  various  degrees  of  thickness,  between 
strata  of  different  kinds  of  rocks.  Sometimes  the  layers 
are  almost  as  thin  as  paper,  and,  on  the  other  hand,  they 
are  sometimes  30,  40,  and  even  60  feet  thick.  Seldom, 
however,  do  they  exceed  eight  feet  in  thickness.  The 
lower  part,  or  floor,  as  we  may  term  it,  of  the  coal  for- 
mation is  limestone ;  but  the  upper  part,  where  the  beds 
of  coal  lie  between  strata  of  rock,  is  made  up  of  sand- 
stones, conglomerates,  shales,  and  limestones.  It  is  this 
upper  portion  that  is  commonly  called  the  coal-measures. 
The  rocks  between  which  the  coal  is  laid  down  do  not 
differ  from  many  rocks  in  other  formations,  but  are  to  be 
distinguished  from  them  only  by  their  fossils.  It  is  their 
life-record  that  indicates  their  proximity  to  coal.  This 
fact  is  of  great  practical  use  in  searching  for  localities  of 
coal,  and  a  disregard  of  it  has  sometimes  occasioned 
needless  expense.  On  this  point  Professor  Hitchcock 
remarks :  "  No  geologist  would  expect  to  find  valuable 
beds  of  coal  in  the  oldest  crystalline  rocks,  but  in  the' 
fossiliferous  rocks  alone ;  and  even  here  he  would  have 
but  feeble  expectations  in  any  rock  except  the  coal  for- 
mation. What  a  vast  amount  of  unnecessary  expense 
and  labor  would  have  been  avoided  had  men  who  had 
searched  for  coal  been  always  acquainted  with  this  prin- 
ciple, and  able  to  distinguish  the  different  rocks !  Per- 
pendicular strata  of  mica  and  talcose  schists  would  then 
never  have  been  bored  into  at  great  expense  in  search 
of  coal ;  nor  would  black  tourmalin  have  been  mistaken 
for  coal,  as  it  has  been."  Commonly,  the  rock  that  lies 
directly  under  a  bed  of  coal  is  clayey  in  its  character, 
and  is  called  the  under-day.  From  its  composition,  and 
from  the  fact  that  roots  of  certain  carboniferous  plants 
are  often  found  in  it,  it  is  inferred  that  it  was  the  dirt- 
bed  in  which  the  plants  grew  that  furnished  the  mate- 
rial for  the  formation  of  the  coal.  The  amount  of  rock 
in  the  strata  of  the  coal-measures  preponderates  vastly 
over  the  amount  of  coal,  the  proportion  being  generally 
fifty  or  more  feet  of  rock  to  one  of  coal. 


216  GEOLOGY. 

311.  Sub-carboniferous  Period. — That  first  part  of  the 
Carboniferous  age  in  which  the  limestone  floor  was  laid 
down  for  the  coal-measures  to  rest  upon  is  called  by  ge- 
ologists the  sub-carboniferous  period.     The  prefix  sub 
being  the  Latin  for  under,  you  see  the  propriety  of  the 
term.     This  floor  was  laid  down  over  a  very  large  area 
in  this  country.     The  same  thing  is  found  in  other  coun- 
tries where  coal  was  made  in  this  age.     The  thickness 
of  this  formation  varies  much  in  different  localities,  in 
some  amounting  to  more  than  6000  feet.     As  this  lime- 
stone was  made  from  the  remains  of  marine  animals, 
crinoids,  corals,  etc.,  long  ages  must  have  been  occupied 
in  constructing  this  foundation  of  the  coral-fields.     The 
strata  of  the  proper  carboniferous  rocks,  the  rocks  of  the 
coal-measures,  are  conformable  with  the  sub-carbonifer- 
ous. 

312.  Sub-carboniferous  Period  in  this  Country. — The 
circumstances  under  which  the  sub-carboniferous  lime- 
stone was  formed  in  the  United  States  have  been  admi- 
rably brought  out  by  Professor  Dana,  and  I  will  attempt 
briefly  to  make  the  principal  of  them  clear  to  you.     In 
the  Niagara  period  of  the  Silurian  age  there  was  a  for- 
mation of  limestone  over  a  large  portion  of  the  interior 
of  the  United  States.     This  was  made  by  the  deposition 
of  the  remains  of  marine  animals.    While  this  was  going 
on  all  the  interior  part  of  the  country  was  a  sea,  not  very 
deep,  but  of  sufficient  depth  for  these  animals.     This 
sea  might  be  considered  as  an  extension  upward  of  the 
present  Gulf  of  Mexico.     It  was  cut  off  from  direct  com- 
munication with  the  Atlantic  Ocean  by  a  low  barrier  of 
land  stretching  from  the  north  downward,  which  had 
been  made  to  emerge  in  order  to  shut  in  this  great  inte- 
rior sea.     A  similar  condition  of  things  existed  in  the 
Devonian  age,  when,  in  the  Upper  Helderberg  period, 
the    corals   were    so   busy  in   laying   down   limestone 
(§  293).     A  similar  arrangement  existed  also  in  the  sub- 
carboniferous  period,  except  that  the  interior  sea  was 


AGE    OF    COAL.  217 

smaller  than  in  the  Devonian,  as  it  was  smaller  then  than 
in  the  Silurian.  It  grew  smaller  from  the  additions 
which  were  made  in  successive  periods  to  the  perma- 
nent land  of  the  continent.  There  was  another  point  of 
difference — in  the  sub-carboniferous  sea  the  crinoids 
were  predominant,  so  that  Dana  speaks  of  it  as  the  Cri- 
noidal  sea,  while  in  the  Devonian  it  was  the  corals  that 
did  most  of  the  work,  and  in  the  Silurian,  brachiopods, 
corals,  and  crinoids  were  about  equally  present. 

313.  How  Coal  was  Made. — All  the  coal  in  the  world 
has  been  formed  from  trees  and  other  plants.  Proof  of 
this  has  been  adduced  in  §  41,  and  need  not  be  dwelt 
upon  now.  The  coal  is  the  result  of  a  decomposition,  to 
a  greater  or  less  degree,  of  the  woody  fibre  or  substance 
of  the  wood.  When  wood  is  burned  in  the  open  air  all 
the  carbon  is  dissipated  by  gaseous  combinations ;  but 
when  the  combustion  is  effected  with  the  air  mostly  ex- 
cluded, the  carbon  is  retained  to  a  considerable  extent, 
making  charcoal.  For  a  full  explanation  of  this  I  refer 
you  to  Part  II.  The  same  changes  that  occur  in  the 
combustion  that  produces  charcoal  may  occur,  under  cer- 
tain circumstances,  without  the  phenomenon  of  combus- 
tion. If,  for  example,  the  decomposition  take  place  slow- 
ly under  water,  the  chemical  changes  are  essentially  the 
same  as  when  what  is  ordinarily  called  combustion  is 
seen.  If  you  observe  what  the  composition  of  wood  is, 
you  can  see  how  this  can  be.  Wood  is  composed  of 
carbon,  hydrogen,  and  oxygen,  the  elements  which  are 
engaged  in  ordinary  combustion  ;  and  it  is  by  the  slow 
action  of  these  upon  each  other  that  the  slow  combus- 
tion under  water  goes  on.  Very  properly,  then,  is  this 
process  called  eremacausis,  this  term  being  made  from 
two  Greek  words,  erema,  slowly,  and  kausis,  burning. 
The  same  thing  occurs  in  the  decay  of  vegetable  matter 
in  the  open  air,  the  slow  combustion  in  this  case  being, 
however,  carried  out  in  full,  as  in  the  ordinary  burning 
of  wood,  the  carbon,  oxygen,  and  hydrogen  all  forming 

K 


218  GEOLOGY. 

gradually  new  combinations,  as  they  do  quickly  in  com- 
mon combustion.  Heat  is  more  or  less  an  agent  in  ef- 
fecting eremacausis,  as  it  is  in  effecting  the  combustion 
which  is  sudden  and  attended  with  palpable  phenomena. 

314.  Condensation  of  Coal  by  Pressure. — While  the 
coal  is  forming  it  is  subjected  more  or  less  to  pressure 
by  the  masses  of  matter  which  accumulate  above  it,  and 
form  the  rocky  strata.     It  is  therefore  condensed,  in- 
stead of  being  light  and  porous,  like  charcoal,  or  the 
coke  which  is  obtained  in  the  making  of  gas.     In  peat 
we  have  an  example  of  the  looseness  of  coal  formation 
when  subjected  to  but  little  pressure. 

315.  Bituminous  and  Non-bituminous  Coal.  —  Anthra- 
cite, or  non-bituminous  coal,  is  almost  pure  carbon,  but 
bituminous  coal  contains  considerable  hydrogen  and  ox- 
ygen.    It  is  the  hydrogen,  in  connection  with  the  car- 
bon, that  produces  its  flame  when  it  is  burned.     The 
flame  is  really  the  burning  of  the  carbureted  hydrogen, 
which  in  our  gas-works  is  evolved  from  bituminous  coal 
by  a  low  degree  of  combustion,  and  is  then  passed  about 
by  pipes  to  be  burned  in  our  houses.     The  flame  which 
plays  over  an  anthracite  fire  when  it  is  not  wholly  kin- 
dled is  the  burning  of  a  different  gas,  which  I  have  no- 
ticed in  Part  II.,  §  67.     It  is  supposed  that  anthracite 
coal  was  once  bituminous,  and  that  it  was  freed  from  its 
bituminous  qualities  by  a  process  essentially  the  same 
with  that  by  which  we  make  gas  in  our  gas-works,  the 
difference  being  simply  that  we  have  left  in  the  one  case 
a  solid  non-bituminous  coal,  and  in  the  other  a  porous 
one — common  coke. 

316.  How  the  Coal  was  Deposited. — You  are  now  pre- 
pared to   see  how  the  coal  was  deposited  in  beds   or 
strata  between  strata  of  rocks.     In  the  first  place  there 
was  a  growth  of  plants  of  various  kinds,  varying  in  size 
from  small  mosses  to  enormous  trees,  in  the  dirt-bed  of 
which  I  have  spoken  in  §  310.     This  was,  for  the  most 
part,  a  swampy  growth,  and  that,  too,  as  you  will  soon 


AGE   OF   COAL.  219 

see,  of  a  most  luxuriant  and  profuse  character.  Trees 
and  shrubs  dropped  their  leaves  and  fruit  year  after  year, 
and  at  length  died  themselves,  while  other  trees  and 
shrubs  took  their  places ;  and  thus  growth  and  decay 
went  on,  perhaps,  through  many  slowly-moving  centu- 
ries, till  enough  of  these  vegetable  remains  was  accumu- 
lated to  make  a  coal-bed.  At  length  a  subsidence  of  the 
land  took  place,  the  water  flowed  over  it,  covering  up  all 
this  accumulation  of  vegetable  substance,  and  under  the 
water  and  the  detritus  which  the  water  brought  in,  the 
decomposition  occurred  which  resulted  in  the  produc- 
tion of  coal.  The  detritus  went  on  accumulating,  at  the 
same  time  slowly  solidifying  from  below  upward,  till  at 
length  the  subsidence  ceased,  and  there  succeeded  an  el- 
evation, so  as  to  bring  the  surface  again  into  the  swampy 
condition  for  a  new  growth,  preparatory  to  another  bed 
of  coal.  The  set  of  processes  thus  described  was  in 
some  cases  many  times  repeated,  there  being  often  many 
beds  of  coal  between  the  strata  of  rock.  In  Kentucky 
there  are  from  fifteen  to  twenty  separate  coal-beds  in 
the  strata,  and  in  Nova  Scotia,  at  a  locality  called  the 
Joggins,  there  are  seventy-six  coal-seams,  some  of  them 
being  very  thin.  The  process  was  essentially  the  same 
for  each  of  these,  the  periods  of  elevation  and  subsidence 
being  longer  for  the  thick  seams  than  for  the  thin  ones. 
Though  there  were  alternate  subsidence  and  elevation, 
"  the  sinking  condition,"  remarks  Hugh  Miller,  "  was  the 
general  one ;  platform  after  platform  disappeared,  as 
century  after  century  rolled  away,  impressing  upon  them 
their  character  as  they  passed ;  and  so  the  coal-meas- 
ures, where  deepest  and  most  extensive,  consist,  from 
bottom  to  top,  ofthese  buried  platforms,  ranged  like  the 
sheets  of  a  work  in  the  course  of  printing,  that,  after  be- 
ing stamped  by  the  pressman,  are  then  placed  horizon- 
tally over  one  another  in  a  pile." 

317.  Impurities  of  Coal. — Coal  varies  much  in  its  pu- 
rity, as  every  one  who  has  burned  coal  must  have  no- 


220  GEOLOGY. 

ticed  from  year  to  year.  The  impurities  came  in  part 
from  the  woody  substance  from  which  the  coal  was 
made.  There  was  silex,  which  is  one  of  the  chief  of  the 
impurities,  in  some  of  the  plants  of  the  Coal  age.  But 
impurities  came  chiefly  from  the  detritus  which  was  laid 
down  upon  the  coal-beds,  for  there  would,  of  course,  be 
more  or  less  admixture  of  this  with  the  coal.  There  is 
more  or  less  iron  pyrites  (sulphuret  of  iron)  in  coal,  and 
to  this  is  owing  the  sulphur  smell  which  a  coal  fire  gives 
out.  When  there  is  much  of  it  in  coal  it  detracts  much 
from  its  value,  causing  it  to  crumble  on  exposure  to  the 
air,  and  to  emit  strong  fumes  when  burned. 

318.  Rate  of  Formation  of  Coal. — Some   calculations 
have  been  made  in  regard  to  the  time  required  for  the 
formation  of  beds  of  coal.     Taking  some   observations 
of  Liebig  as  to  the  rapidity  of  vegetable  accumulation, 
it  has  been  calculated  that  it  would  require  170  years  to 
make  one  inch  thickness  of  anthracite  coal,  and  there- 
fore 122,400  years  to  accumulate  a  stratum  of  60  feet. 
This  is  based  upon  the  ordinary  growth  of  the  present 
time  ;  but,  as  you  will  soon  see,  the  growth  of  the  Car- 
boniferous age  was  probably  much  more  rapid  than  it  is 
now,  and  this,  of  course,  must  reduce  the  time.     But,  at 
any  rate,  the  time  must  have  been  very  long  for  the  ac- 
cumulation of  even  a  bed  of  ordinary  thickness.     And 
when  we  come  to  take  into  the  account  the  formation 
of  the  rocky  strata  as  well  as  the  coal-beds,  our  arithme- 
tic must  give  out,  for  the  whole  system,  from  the  sub- 
carboniferous  upward,  through  all  the  strata,  has  a  thick- 
ness, in  some  cases,  of  from  12,000  to  about  15,000  feet 
— that  is,  nearly  three  miles. 

319.  Plants. — The  remains  of  plants  are  found  in  great 
abundance  in  the  coal-measures,  though  none  appear  in 
the  great  sub-carboniferous  limestone  floor  which  is  be- 
neath them.     The  plants  were  of  various  sizes.     Many 
of  them  were  prodigious  in  size,  compared  with  similar 
kinds  of  plants  at  the  present  day.     The  vegetation  of 


AGE   OF    COAL. 


221 


Fig.  122. 


that  age  was  to  a  large  extent,  in  point  of  size,  a  forest 
vegetation,  and  yet  but  few  of  the  plants  which  at  the 
present  time  are  of  the  same  family  with  the  largest  that 
existed  then  are  a  little  taller  than  a  man.  The  remains 
found  are  of  various  kinds — trunks, 
branches,  pieces  of  bark,  cones, 
leaves,  etc.  The  impressions  of 
leaves  upon  the  laminae  of  rock  are 
sometimes  very  beautiful,  as  seen  in 
Fig.  122.  Here  we  have  a  carbon- 
aceous representation  of  the  stem 
and  leaves — that  is,  the  carbon  of 
the  plant  in  the  decomposition  of 
the  vegetable  substance  is  left  upon 
the  stone.  "  The  shaly  beds,"  says 
Dana,  "often  contain  the  ancient 
ferns  spread  out  between  the  lay- 
ers with  all  the  perfection  they 
would  have  in  a  herbarium,  and  so  abundantly  that, 
however  thin  the  shale  be  split,  it  opens  to  view  new  im- 
pressions of  plants."  The  experiments  of  Professor  Gop- 
pert,  of  Breslau,  go  far  to  explain  the  various  conditions 
in  which  we  find  the  remains  of  plants  in  the  rocks  of 
the  coal-measures.  He  placed  fern-leaves  in  clay,  and 
when  they  had  become  dry  exposed  them  to  a  red  heat, 
and  thus  obtained  striking  resemblances  to  the  fossil 
ferns  in  the  rocks.  According  to  the  degree  of  heat,  the 
leaves  were  found  to  be  either  brown,  shining,  black,  or 
entirely  lost,  the  impression  alone  remaining.  In  this 
latter  case  the  carbon  of  the  leaves,  being  diffused  in  the 
clay,  stained  it  black,  thus  showing  that  the  color  of  the 
coal-shales  is  derived  from  the  carbon  of  the  plants  in- 
closed in  them.  I  will  now  proceed^lQ^notice  some  of 
the  plants  of  this  age. 

320.  Calamites. — This  is  a  name  given  to  a  family  of 
plants  that  belong  to  the  same  tribe  with  the  horse-tails, 
cat-tails,  and  rushes  of  the  present  day.  Two  species 


222  GEOLOGY. 

are  represented  in  Fig.  123,  b  being  the  same  with  a,  but 


Fig.  13a 

showing  remains  of  its  roots.  The  plant  is  jointed  and 
hollow,  the  surface  being  deeply  fluted.  While  the 
rushes  and  cat-tails  of  the  present  day  are  quite  small, 
some  specimens  of  these  ancient  plants  have  been  found 
20,  and  even  40  feet  in  length,  and  three  feet  in  diameter. 
Portions  of  the  trunks  of  these  trees,  for  so  they  may  be 
called,  have  been  found  standing  upright  in  coal  mines, 
penetrating  the  sandstone  layers  above  the  coal. 

321.  Sigillaria  and  Stigmaria. — These  were  for  a  long 
time  supposed  to  be  two  distinct  plants,  but  they  have 
been  found  to  belong  to  the  same  plant,  the  Sigillaria  be- 
ing the  trunk,  and  the  Stigmaria  the  lower  part  of  the 
trunk,  with  the  roots.  The  Stigmaria,  Fig.  124,  is  never 
found  any  whea^but  in  the  under  clay  spoken  of  in 
§  310.  The  trunks  of  the  plant  are  generally  found  lying 
horizontally,  but  sometimes  they  are  erect.  They  vary  in 
length  from  five  to  sixty  feet,  and  in  diameter  from  a 
few  inches  to  five  feet. 


AGE    OF   COAL. 


223 


Fig.  124. 

322.  Lepidodendron. — This  is  a  name  which  has  been 
given  to  a  tribe  of  carboniferous  plants  that  were  much 
like  the  club-mosses  of  the  present  day ;  but  they  were 
lofty,  woody  trees.     One  was  found  in  a  coal  mine  in 
England  that  was  40  feet  long,  and  so  enormously  large 
at  the  base  as  to  measure  13  feet  in  diameter. 

323.  Ferns. — There  was  a  great  abundance  of  ferns  in 
the  Carboniferous  age.     A  very  large  number  of  species 
have  been  found  in  the  coal  strata.     In  Figs.  125, 126, 


Figs.  125, 126. 


127,  and  128  (p.  224)  are  represented  some  fossil  ferns. 
The  two  first  are  from  the  coal-measures  of  Rhode  Isl- 


224 


GEOLOGY. 


Ffg.  127. 


Fig.  128. 


and.  Many  of  the  ferns  were  trees  resembling  the  tree- 
ferns  now  found  in  some  tropical  countries,  growing  to 
the  height  sometimes  of  even  40  and  50  feet.  It  is  stated 
by  Hitchcock  that  over  250  species  of  ferns  have  been 
found  in  the  coal  strata  of  Europe,  and  yet  the  native 
species  in  Europe  at  the  present  time  do  not  exceed  50. 
As  ferns  are  now  far  more  abundant  in  tropical  than  in 
temperate  regions,  the  life-record  of  the  coal-measures 
seems  to  show  that  the  climate  in  Europe  and  this  coun- 
try during  the  coal  period  was  tropical. 

324.  Conifers. — The  Conifers,  or  cone-bearing  plants, 
were  very  abundant.     These  are  Gymnogens,  or  dicotyl- 
edonous plants  (Fig.  87),  related  to  the  pines  and  yews. 
Most  of  the  other  plants  of  this  age  were  Acrogens 
(Fig.  86),  the  Ferns,  the  Equisetacea3,  or  cat-tail  family, 
and  the  Lycopodiacese,  or  club-mosses.    The  Amphigens 
(Fig.  85)  were  represented  in  sea-weeds  and  a  few  mush- 
rooms.    It  is  doubtful  whether  there  were  «my  Endo- 
gens   (Fig.  88),  and  there  were  none  of  the  Exogens 
(Fig.  91),  the  chief  foresktrees  and  shrubs  of  the  present 
day. 

325.  General  View  of  Carboniferous  Vegetation. — In 
Fig.  129  you  have  grouped  together  many  of  the  differ- 
ent kinds  of  plants  of  the  Carboniferous  age.     On  the 
right,  in  the  foreground,  is  the  Sigillaria,  with  Stigmaria 


AGE    OF    COAL. 


225 


Fig.  129. 

roots,  and  next  to  it  the  beautiful  tree-fern.  On  the  left, 
standing  up  loftily,  is  a  Lepidodendron,  and  by  it  lies 
prostrate  a  Calamites,  there  being  also  in  the  rear  of  it, 
in  the  background,  one  inclining  of  a  much  larger  size. 
The  smaller  plants  fill  up  the  intervals  between  these, 

K2 


226  GEOLOGY. 

There  were  few,  if  any  flowers  in  all  this  vegetation,  but 
"  what  was  wanting  in  blossom,"  says  Page,  *  was  more 
than  compensated  for  by  the  profusion  of  light,  symmet- 
rical, feathery  fronds,  and  by  the  tall,  pillar-like  stems 
which  rose,  each  one  boldly  carved  with  its  own  pecul- 
iar pattern.  The  trunks  of  a  modern  forest  are  rough 
and  gnarled;  those  of  the  period  now  under  review 
sprang  up  like  the  sculptured  shafts  of  a  medieval  tem- 
ple, graceful  in  proportion,  and  rich  in  ornament  through 
the  endless  repetition  of  flutings,  spirals,  zigzags,  loz- 
enges, ovals,  and  other  geometrical  designs — these  de- 
signs being  the  persistent  leaf-scars  of  a  vegetation  sim- 
pler in  structure  and  more 
primitive  in  plan."  An  exam- 
pie  of  the  leaf-scars  of  which 
he  speaks  is  represented  in 
Fig.  130,  the  scars  left  by  the 
fallen  leaves  being  seen  at  a, 
while  at  b  is  the  surface  of 
the  wood  brought  to  view  by 
the  removal  of  the  carbon- 
Fig- m  ized  bark.  You  observe  the 

regularity  with  which  these  scars  are  arranged.  The 
modes  of  this  regularity  differ  in  different  plants,  thus 
affording  a  rich  variety. 

326.  Causes  of  the  Rank  Carboniferous  Vegetation. — 
In  order  to  understand  how  the  rank  vegetation  of  that 
age  was  produced,  you  must  recur  to  what  I  said  of  the 
chemistry  of  the  atmosphere  in  Part  II.  You  there 
learned  that  from  the  carbonic  acid  gas  which  is  sup- 
plied to  the  air  from  the  lungs  of  animals,  from  fires,  and 
from  various  chemical  decompositions,  the  leaves  gather 
in  the  most  of  the  carbon  which  is  incorporated  in  the 
plants  in  their  growth.  Now  it  is  supposed  that  there 
was  much  more  carbonic  acid  in  the  atmosphere  up  to 
the  beginning  of  the  coal-making  age  than  there  was  at 
its  close.  Some  estimate  it  as  having  been  six  times  as 


AGE    OP    COAL.  227 

much  as  it  is  at  the  present  time.  Here,  then,  there  was 
in  the  air  a  large  surplus  of  one  of  the  three  materials 
of  which  plants  are  chiefly  composed,  and  it  was  appro- 
priated in  producing  the  profuse  vegetation.  And  as 
this  vegetation  was  for  the  purpose  of  making  coal,  we 
may  say  that  the  material  for  the  coal  was  kept  in  the 
atmosphere  in  a  gaseous  state,  by  being  combined  with 
oxygen,  until  the  earth,  during  a  lapse  of  long  ages,  was 
put  into  a  fit  condition  to  bring  forth  an  exuberant  veg- 
etation. When  this  was  effected  the  Creator  introduced 
the  requisite  plants,  and  the  transfer  was  made  from  the 
atmosphere  through  them  to  the  coal-measures.  Such 
a  transfer  from  the  gaseous  to  the  solid  state  of  such  a 
quantity  of  matter  seems  at  first  thought  strange,  but  it 
is  no  more  so  Jthan  the  transformation  which  we  see  con- 
tinually in  the  case  of  water.  This  rises  in  the  vaporous 
or  gaseous  state  into  the  atmosphere  by  evaporation, 
and  anon  we  see  some  of  it  again  in  the  shape  of  solid 
ice  on  the  surface  of  the  earth. 

327.  Climate  of  the  Carboniferous  Age. — The  climate 
of  the  earth  was  very  different  in  that  age  from  what  it 
is  now.     It  was  warm  in  all  quarters,  and  very  equally 
so.     We  know  this  because  we  find  very  widely  distrib- 
uted the  remains  of  plants  and  animals  similar  to  those 
which  now  flourish  in  warm  climates.     The  climate  was 
so  warm  in  the  arctic  regions  that  rank  vegetation  was 
present  there,  and  coal  was  laid  down.    With  such  prev- 
alent warmth  there  must  have  been  great  moisture  in 
the  air,  and  this  favored  rank  growth,  notwithstanding 
there  probably  was  from  this  moisture  less  of  clear  sun- 
shine than  there  is  now. 

328.  Carboniferous  Scenery. — Though  the  vegetation 
of  that  age  was  so  rich,  the  scenery  was  tame  and  mo- 
notonous.     Forests,  with   their   tangled  undergrowth, 
mostly  swampy,  spread  over  vast  platforms,  in   some 
cases  almost  continental  in  extent.     There  were  no  such 
elevations  as  we  see  at  the  present  day  to  relieve  the 


228  GEOLOGY. 

eye,  but  one  wide  wilderness  stretched  far  away,  varied 
only  by  slight  undulations.  We  may  get  some  idea  of- 
the  nature  of  this  scenery  from  some  localities  on  our 
earth,  but  none  at  all  of  its  extent.  Especially  extensive 
were  the  platforms  in  the  earlier  part  of  the  Carbonifer- 
ous age,  for  the  beds  of  coal  then  laid  down  are  found 
to  be  much  vaster  in  extent  than  those  of  the  later  coal- 
measures.  In  this  country  these  early  beds  cover  a  large 
portion  of  the  continent.  Each  of  the  successive  plat- 
forme  of  luxuriant  vegetation,  after  having  maintained 
the  same  level  for  hundreds,  or  even  thousands  of  years, 
was  submerged  in  water  gradually  (Hugh  Miller  thinks 
in  some  cases  suddenly),  that  each  bed  of  coal  might  be 
packed  down  with  layers  of  rock  above  it.  The  wide 
wilderness  of  vegetation  thus  became  a  wide  waste  of 
waters. 

329.  Animals. — So  highly  charged  with  carbonic  acid 
gas  was  the  atmosphere  of  the  coal-making  age,  that  an- 
imals which  require  such  air  as  we  now  have  on  the 
earth  could  not  exist.  There  were,  therefore,  no  mam- 
mals or  birds,  and  none  of  the  higher  kinds  of  insects. 
There  were  cold-blooded  animals,  as  fishes  and  reptiles, 
the  latter  finding  their  appropriate  localities  in  the  stag- 
nant pools,  swamps,  and  thick,  damp  forests  of  that  age. 
Cold-blooded  animals  live  an  inactive,  lazy  life,  as  com- 
pared with  the  warm-blooded,  and  therefore  do  not  re- 
quire so  much  oxygen.*  There  was,  of  course,  an  abund- 
ance of  Mollusks,  Crustaceans,  and  Radiates,  especially 
when  the  platforms  were  submerged,  and  the  limestone 
strata  were  forming.  The  tameness  and  monotony  of 

*  It  would  seem  at  first  thought  that  the  life  of  fishes  is  generally  a 
very  active  one ;  but  it  is  not  so,  for  the  fish  needs  to  make  but  little 
effort  in  its  motions,  for  two  reasons.  First,  it  is  of  nearly  the  same 
specific  gravity  with  the  element  in  which  it  moves,  and  is  therefore 
obliged  to  make  but  a  slight  effort  in  any  upward  movement.  It  is 
in  strong  contrast  with  birds  in  this  respect.  Secondly,  most  fishes 
have  an  air-bladder,  which  they  can  compress  or  enlarge  at  pleasure, 
as  they  wish  to  fall  or  rise.  See  my  Natural  History,  Chapter  xx. 


AGE    OF   COAL. 


229 


the  carboniferous  scenery  were  heightened  by  the  ab- 
sence of  all  running  and  flying  animals.  As  to  sounds, 
"  there  was  no  music  in  the  groves,"  says  Dana, "  save, 
perhaps,  that  of  insect  life  and  the  croaking  Batrachian." 
330.  Coral  Animals. — The  reef-making  animals,  some 
varieties  of  which  you  see  in  Fig.  131,  were  busy  wher- 


^^  w 

1.  Syringopera.    2.  Lythostrotion.    3.  Aulopora.    4.  Amplexus.    5.  Clisiophyl- 
lum.     6.  Ptilopora.    7.  Archimedopora. 

Fig.  131." 

ever  limestone  was  forming.  They  had  a  large  work  to 
do,  then,  in  the  sub-carboniferous  period,  when  the  great 
limestone  floor  was  laid  down  for  the  coal-measures,  and 
afterward,  also,  in  the  case  of  those  strata  over  the  coal- 
beds  which  are  composed  of  limestone. 

331.  Crinoids  and  Sea-urchins. — These  animals  abound- 
ed in  connection  with  the  corals,  the  crinoids  being  much 
more  abundant  than  the  corals  in  the  limestone  of  the 
sub-carboniferous  period.  Indeed,  whole  strata  are  com- 
posed of  the  calcareous  remains  of  the  crinoids.  Two 


230  GEOLOGY. 

varieties  are  represented  in  Fig.  132,  at  1  and  2.     There 


Fig.  132. 


is  also  one  variety  of  sea-urchin  at  3,  and  the  plates  and 
spine  of  another  variety  at  4.  Fig.  133  represents  a  slab 
of  limestone  from  Iowa,  in  which  are  seen  remains  of  cor- 


Fig.  133. 


AGE    OF   COAL. 


231 


als,  crinoids,  etc.,  brought  out  in  relief  by  the  long-con- 
tinued action  of  the  weather  upon  the  stone. 

332.  Articulates. — Of  the  Crustaceans,  but  few  of  those 
singular  animals,  the  Trilobites,  which  numbered  about 
six  hundred  species  in  the  Silurian,  were  present  in  the 
Carboniferous  age,  and  these  were  the  last  of  that  tribe. 
New  tribes  appeared,  of  which  one  was  very  much  like 
the  horse-shoe  of  the  present  day.     Minute  Crustaceans 
swarmed  in  myriads  in  stagnant  waters,  as  their  remains 
in  the  rocks  now  show.     Of  insects  there  have  been 
found  some  wing-cases  of  beetles.     Insects  of  the  cock- 
roach tribe  nourished  then,  and  there  were  also  some 
scorpions. 

333.  Reptiles  and  Fishes. — Some  reptiles  appeared  in 
this  age,  foreshadowing  the  succeeding  one,  in  which 
they  were  to  be  so  abundant  and  large  as  to  give  the 
name  of  Reptilian  to  it.     The  remains  of  some  have  been 
found,  and  tracks  have  been  discovered  which  evidently 
belonged  to  reptiles,  no  remains  of  which  have  as  yet 
appeared  in  the  rocks.     Fig.  134  represents  two  of  the 

tracks  of  such  a  reptile,  which 
were  found  near  Pottsville,  in 
Pennsylvania,  by  Dr.  Isaac  Lea, 
of  Philadelphia.  In  one  part  of 
the  slab  there  is  the  impression 
of  a  tail.  These  marks,  mingled 
with  ripple-marks  and  impres- 
sions of  rain-drops,  making  out 
a  most  interesting  record  of  that 
age  so  far  distant  in  the  past 
eternity,  have  been  before  no- 
ticed in  §  210.  Some  of  the 
fishes  of  this  age  foreshadow 
the  succeeding  Reptilian  age, 
by  combining  some  of  the  reptilian  characteristics  with 
those  of  fishes.  Of  such  reptile  fishes  there  is  at  the  pres- 
ent time  but  one  known  genus,  the  Lepidosteus,  or  gar- 


Fig.  134. 


232  GEOLOGY. 

pike  of  North  America.  Of  this  Hugh  Miller  says  that 
"  it  would  almost  seem  as  if  it  had  been  spared,  amid 
the  wreck  of  genera  and  species,  to  serve  us  as  a  key  by 
'which  to  unlock  the  marvels  of  the  ichthyology  of  those 
remote  periods  of  geologic  history  appropriated  to  the 
dynasty  of  the  fish."  This  wonderful  animal  has  an  ar- 
mor of  bony  scales,  covered  with  hard  enamel  like  that 
of  teeth,  so  that  it  would  be  difficult  for  any  shot  to  take 
effect  on  it ;  and  as  his  teeth  are  very  formidable,  it  has 
been  said  of  him  by  the  fisherman  that  "  he  can  hurt  ev- 
ery thing,  and  nothing  can  hurt  him."  It  is  very  agile, 
darting  through  the  water  even  up  the  rapids  of  Niaga- 
ra. It  can  bend  its  head  freely  in  all  directions,  like  a 
serpent,  which  no  other  fish  can  do,  for  its  vertebra  have 
the  ball  and  socket  arrangement  of  serpents  instead  of 
the  cup  arrangement  of  fishes.  In  this  fish  we  have  the 
only  living  type  of  the  prevailing  family  of  fishes  in  the 
Coal  period.  Some  of  the  fishes  of  that  family  were 
such  monsters  in  size,  compared  with  the  gar-pike,  that 
the  sublime  language  of  Job  about  the  Leviathan  could 
be  properly  applied  to  them.  Hugh  Miller  says  of  them, 
"If  the  gar-pike,  a  fish  from  three  to  four  feet  in  length, 
can  make  itself  so -formidable  from  its  great  strength  and 
activity,  and  the  excellence  of  its  armor,  that  even  the 
cattle  and  horses  that  come  to  drink  at  the  water's  side 
are  scarce  safe  from  its  attacks,  what  must  have  been  the 
character  of  a  fish  of  the  same  reptilian  order  from  thirty 
to  forty  feet  in  length,  furnished  with  teeth  thrice  larger 
than  the  largest  alligator,  and  ten  times  larger  than  the 
bulkiest  Lepidosteus,  and  that  was  covered  from  snout 
to  tail  with  an  impenetrable  mail  of  enameled  bone  ?" 

334.  Mollusks. — Of  these  there  was  a  great  abundance 
and  variety.  The  Brachiopods  were  largely  represented. 
Of  the  genus  Productus  there  were  many  species,  one  of 
which  is  represented  in  Fig.  135.  It  is  called  Productus 
spinulosus,  from  the  long,  slender  spines  that  project  from 
the  shell.  Of  another  genus  of  the  Brachiopods,  Spirifcr, 


AGE   OF   COAL. 


233 


Fig.  135. 


there  were  also  many  spe- 
cies. One  of  them  is  repre- 
sented in  Fig.  136,  show- 
ing the  spiral  support  from 
which  it  takes  its  name,  a, 
as  it  is  in  the  shell,  and  #, 
a  part  of  it  taken  out.  The 
strange  Orthoceratites, 
which,  like  the  Crustacean 
Trilobites,  were  abundant 
in  the  Silurian  age,  now, 
like  them,  appeared  with 
but  few  species,  and,  be- 
fore the  age  had  passed, 
became  extinct. 


Fig.  ISO. 

335.  Permian  Period. — The  Carboniferous  age  ended 
with  what  is  called  the  Permian  period,  in  which  no  coal 
was  formed.  This  period  has  its  name  from  a  portion 
of  Russia  which  was  in  ancient  times  the  kingdom  of 
Perraia.  Here  the  rocks  of  that  period  cover  an  area 
TOO  miles  long  and  400  broad.  Until  quite  recently,  it 
was  supposed  that  there  are  no  Permian  strata  in  this 
country ;  but  they  have  been  discovered  in  Illinois,  Kan- 
sas, and  some  parts  of  the  slope  of  the  Rocky  Mountains. 
In  this  period  nearly  all  the  country  east  of  the  Mississip- 
pi was  dry  land,  and  therefore  all  the  Permian  deposits 
were  made  on  the  west  of  it,  with  the  exception  of  a  small 
part  of  Illinois.  In  Europe  there  are  Permian  strata  in 
Central  Germany,  and  in  England  in  the  neighborhood 
of  the  coal  regions,  in  addition  to  the  extensive  area  cov- 


234  GEOLOGY. 

ered  by  them  in  Russia.  In  this  country  the  rocks  are 
limestones,  sandstones  of  various  colors,  shales  or  marls, 
gypsum  beds,  and  conglomerates.  In  the  Permian  stra- 
ta of  Europe  the  limestones  are  mostly  found  to  be  mag- 
nesian.  Why  this  is  so  the  researches  of  geologists  have 
as  yet  not  been  able  to  determine ;  and  Phillips  remarks 
in  regard  to  it  that "  we  must  be  content  to  shelter  our 
ignorance  under  the  statement  that,  from  some  unknown 
cause,  the  waters  of  the  sea  were  then  decomposed  in 
such  a  way  as  to  permit  very  generally  the  precipitation 
of  united  magnesian  and  calcareous  carbonates." 

336.  North  America  at  the  Close  of  this  Age.— Two 
thirds  of  the  North  American  Continent  was  above  the 
level  of  the  ocean  at  the  close  of  the  Carboniferous  age. 
This  was  the  eastern  part,  while  the  western  was  occu- 
pied by  a  large  interior  or  mediterranean  sea,  such  as  in 
the  Silurian  and  Devonian  ages  extended  over  much  of 
the  eastern  part  also.     The  Rocky  Mountains,  as  well 
as,  indeed,  the  Alleghanies,  did  not  yet  exist.     The  bor- 
ders or  fringes  of  the  continent  on  the  south  and  east 
were  yet  to  be  added,  and  also  a  large  portion  of  the 
western  part  of  the  continent.    Florida,  that  great  work 
of  the  coral  animals,  was  yet  to  be  constructed.     Al- 
though so  much  was  done,  long  ages  upon  ages  were  yet 
to  be  passed  before  the  continent  would  be  completed. 

337.  Disturbances  in  the  Coal-measures. — The  strata 
of  the  Carboniferous  age  have  been  subjected  to  upheav- 
als, foldings,  fractures,  etc.,  like  all  other  strata,  some  of 
them  being  very  extensive,  even  mountainous.    If  it  were 
not  for  these,  few  of  the  beds  of  coal  lying  between  the 
thousands  (§318)  of  feet  of  strata  would  have  come  with- 
in the  reach  of  man  in  his  minings.     Most  of  these  up- 
heavals and  flexures  occurred  at  the  close  of  the  age,  in 
the  interval  between  Palaeozoic  and  Mesozoic  time.     The 
results  are  so  observable  in  this  country,  all  along  the  re- 
gion of  the  Appalachian  chain,  that  the  change  produced 
at  that  time  has  been  called  the  Appalachian  revolution. 


AGE    OF   COAL.  235 

Where  the  flexures  are  most  decided  the  strata  were  met- 
amorphosed— gneiss,  granite,  and  other  crystalline  rocks 
being  produced — showing  that  great  heat  was  present  at 
that  time  in  such  localities.  The  same  changes  took  place 
in  the  coal-measures  of  other  countries.  The  movements 
in  the  bending  and  folding  of  the  strata  were  not  con- 
fused, but  occurred  in  certain  lines,  according  to  some 
systematic  plan  of  the  Creator.  They  were  probably 
very  slow — perhaps  to  the  extent  of  some  yards,  or  even 
feet  only,  in  a  century — else  such  bend  ings  without  frac- 
tures as  are  often  found  could  not  have  been  produced. 
It  is  believed  that,  besides  the  metamorphosis  of  strata 
which  laid  up  at  that  time  for  the  use  of  man  such  quan- 
tities of  building  material,  there  were  separated  and  de- 
posited in  this  metamorphic  process  many  of  the  precious 
and  other  metals,  and  also  many  of  the  precious  gems.  It 
has  also  been  observed  that  the  coal  is  most  debitumin- 
ized  where  the  disturbances  of  the  strata  were  the  great- 
est. This  is  probably  to  be  attributed  to  two  causes — 
the  action  of  great  heat  in  such  localities,  and  the  oppor- 
tunity of  escape  for  gaseous  products  given  by  the  frac- 
tures made  in  the  disturbances.  Denudation  is  often 
connected  with  the  faults,  bendings,  etc.  This  is  exem- 
plified in  Fig.  68,  p.  140.  These  denudations  were  some- 
times vast,  the  thickness  of  strata  removed  amounting 
even  to  many  thousands  of  feet. 

338.  Palaeozoic  Life-record.  —  You  have  now  been 
made  acquainted  to  some  extent  with  the  changes  in  life 
which  occurred  in  the  three  Paleozoic  ages — the  Siluri- 
an, Devonian,  and  Carboniferous.  While  the  grand  di- 
visions marked  out  by  the  Creator  are  preserved  from 
the  beginning,  showing  that  the  same  general  plan  exist- 
ed from  the  outset  as  now,  the  predominant  forms  of 
life,  especially  of  animal  life,  are  very  different  from  each 
other  in  the  different  ages,  and  very  different  from  those 
which  appear  at  the  present  time.  All  the  four  divisions 
of  animals  began  in  the  first  of  the  Palaeozoic  ages,  the 


236  GEOLOGY. 

">^^ 

SilurialTpbut  "the  vertebrates  did  not  appear  till  the  lat- 
ter part  of  it,  and  then  in  small  numbers,  and  only  in  the 
low  form  of  fishes.  Reptiles  did  not  appear  till  the  lat- 
ter part  of  the  Devonian,  the  age  of  Fishes,  and  were  not 
in  their  greatest  abundance  till  after  the  Paleozoic  time 
was  past.  There  were  no  Mammals  in  the  Paleozoic 
ages.  Many  species  of  animals  which  flourished  in  those 
ages,  perhaps  largely,  at  length  vanished,  never  to  ap- 
pear again ;  for  it  is  a  remarkable  fact,  that  any  species 
which  conies  to  an  end  is  never  again  brought  upon  the 
stage.  For  example,  the  Trilobites,  of  which  there  were 
hundreds  of  species  in  the  Silurian  age,  all  dwindled 
away  one  after  another,  till,  in  the  Carboniferous  age,  the 
last  of  the  species  disappeared,  and  none  of  all  of  them 
has  ever  again  been  revived.  At  the  close  of  the  Car- 
boniferous age,  in  the  midst  of  the  disturbances  that  oc- 
curred, every  species  of  animal  and  plant  was  destroyed, 
though  many  species  belonging  to  the  same  genera  with 
those  of  this  age  existed  in  the  after  ages.  This  uni- 
versal destruction  of  the  life  of  the  Carboniferous  age  is 
one  of  the  great  marks  of  distinction  between  this  and 
the  following  age. 


CHAPTER    XVII. 

AGE    OF   REPTILES. 

339.  Names. — We  now  pass  from  Paleozoic  to  Meso- 
zoic  time,  or  the  Medieval  age  of  the  earth,  the  age  of 
Reptiles.  It-  is  divided  into  three  periods,  the  Triassic, 
Jurassic,  and  Cretaceous.  The  Triassic  is  so  called  on 
account  of  an  obvious  threefold  division  which  the  sys- 
tem of  rocks  presents  in  Germany,  though  it  is  not  seen 
in  other  quarters  of  the  world.  The  term  Jurassic  comes 
from  the  Jura  Mountains  of  Switzerland,  where  the  for- 
mation or  system  of  strata  designated  by  this  name  is 
well  developed,  and  has  been  particularly  examined. 


AGE   OF   RE 

The  term  Oolitic  is  sometimes  appli< 
monly  it  is  confined  to  one  portion  only  of  the  Jurassic 
period,  in  which  one  of  the  limestones  formed  is  oolitic 
in  its  structure.  The  term  Cretaceous,  from  the  Latin 
word  creta,  chalk,  is  applied  to  the  closing  period  of  the 
Reptilian  age,  because  the  chalk  of  England  and  Europe 
is  one  of  the  rocks  of  the  system  belonging  to  that  pe- 
riod. In  this  country  we  have  the  system,  but  the  chalk, 
which  is  so  prominent  in  those  countries,  is  left  out  here. 

340.  Triassic  Rocks. — The   rocks   of  this  period  are 
mostly  sandstones,  shales,  conglomerates,  and  sometimes 
some  limestones.     So  prominent  are  the  red  sandstones 
that  the  whole  system  is  called  the  New  Red  Sandstone, 
in  distinction  from  the  Old  Red  Sandstone  of  the  Devo- 
nian age.     In  the  valley  of  the  Connecticut  the  material 
for  the  rocks  of  this  formation  was  derived  from  the 
crystalline  rocks  in  the  neighborhood,  chiefly  by  the  ero- 
sive action  of  water.     The  freestone  of  Connecticut  and 
New  Jersey,  so  much  used  in  building,  comes  from  this 
formation.     In  the  western  part  of  this  country  the  Tri- 
assic rocks  are  sandstones  and  marls  of  a  brick-red  color, 
often  having  gypsum  in  them.     The  red  color,  so  preva- 
lent in  the  sandstones,  though  varying  much  in  shade,  is 
owing  to  the  presence  of  oxyd  of  iron.     The  life-record  in 
the  rocks  of  this  formation  is  scanty,  because  they  are 
not  well  suited  to  the  preservation  of  fossils. 

341.  Localities. — In  the  eastern  part  of  this  country 
the  Triassic  rocks  are  surface  rocks  along  between  the 
Appalachians  and  the  Atlantic  coast.     In  the  Connecti- 
cut Valley  they  extend  from  the  Sound  at  New  Haven 
up  to  the  northern  part  of  Massachusetts.     There  stand 
up  in  the  midst  of  them  Mount  Holyoke,  Mount  Tom, 
East  and  West  Rock,  and  other  Trappean  elevations, 
imparting  variety  and  grandeur  to  the  scenery.     In  the 
West  this  system  is  extensively  spread  over  part  of  the 
slopes  of  the  Rocky  Mountains.     The  Triassic  system  is 
developed  in  various  parts  of  Europe  and  in  England. 


238  GEOLOGY. 

342.  Triassic  Salt. — While  in  this  country  the  chief 
source  of  salt  is  in  the  Silurian  formation  (§  278),  in  En- 
gland and  Europe  it  is  in  the  Triassic  system,  which  is 
often,  for  that  reason,  called  the  Saliferous  system.    The 
rocks  in  connection  with  which  the  salt  is  found  are  sim- 
ilar in  both  formations,  but  the  manner  in  which  the 
salt  was  produced  could  not  be  the  same  in  both  cases. 
The  evaporating  process  which  it  is  supposed,  as  stated 
in  §  278,  produced  it  in  the  Silurian  formation  in  New 
York,  could  not  in  any  way  accumulate  masses  of  rock 
salt  40  yards  in  thickness,  or  a  mountain  of  salt  600  feet 
high  and  1 200  broad,  such  as  is  found  at  Cordova,  in  Spain. 
It  is  supposed  that  volcanic  agency  operated  in  such 
cases,  as  salt  is  common  in  what  is  thrown  out  from  vol- 
canoes, and  salt-springs  sometimes  rise  to  the  surface 
from  granitic  rocks,  showing  that  there  are  sources  of 
salt  lying  deep  in  the  earth.     The  purity  of  the  rock- 
salt,  it  is  thought,  indicates  its  volcanic  origin,  for  if  it 
were  deposited  from  a  solution  it  would  have  impurities 
mingled  with  it. 

343.  Plants  of  the  Triassic  Period. — Though  the  plants 
which  were  peculiar  to  the  Carboniferous  age  were  not 
present,  as  the  Sigillaria   and  the  Lepidodendrons,  yet 
there  were  Cycads  as  there  were  then,  and  Ferns,  Equi- 
seta,  and  Conifers  in  new  forms.     Trunks  of  conifers  of 
considerable  size  have  been  met  with  in  the  sandstones. 
Some  coal  has  been  found  in  this  formation  in  some  lo- 
calities, made,  of  course,  out  of  the  vegetation  of  which  I 
have  spoken.     Triassic  coal  has  been  discovered  in  Vir- 
ginia and  North  Carolina  in  this  country,  in  Australia, 
and  in  various  parts  of  Asia. 

344.  Animals. — The  excess  of  carbonic  acid  that  ex- 
isted in  the  atmosphere  previous  to  the  Carboniferous 
age  was  removed  from  it  by  the  rank  vegetable  growth 
of  that  period,  so  that  when  the  Triassic  period  came  on 
the  air  was  fitted  for  air-breathing  animals.     They  ac- 
cordingly were  introduced  upon  the  scene.     Not  only 


AGE    OF    REPTILES. 


239 


were  reptiles,  and  among  them  the  monstrous  Saurians, 
introduced,  but  also  birds  and  mammals.  The  mammals 
were  not,  however,  in  great  abundance,  and  were  of  the 
lower  orders,  the  marsupial,  which  at  the  present  day 
are  so  common  in  Australia.  The  fishes  were  all  ganoids 
and  placoids,  as  in  the  Palaeozoic  ages,  but  there  was  an 
approach  in  their  tails  to  the  bilobed  character  of  the 
present  day  (§  302),  and  some  were  wholly  of  this  mod- 
ern fashion.  Of  the  Mollusks,  a  family  called 
Ammonites,  which  figured  largely  in  the  two 
other  periods  of  the 
Reptilian  age,  now  ap- 
peared. One  species, 
the  Ammonites  'nodo- 
sus,  is  represented  in 
Fig.  137.  Among  the 
radiated  animals  of  this 
period  was  a  crinoid  of 
singular  beauty,  called 
the  Lily  Encrinite,  Fig.  138. 

345.  Reptiles.  —  Lizards,  Saurians,  Batra- 
chians,  many  of  them  gigantic  in  size,  were  Fis- 13S- 
abundant,  though  not  so  abundant,  and  strange,  and 
monstrous  as  they  were  in  the  following  period,  the  mid- 
dle one  of  the  age  of  Reptiles.  One  of  the  most  remark- 
able of  these  animals  was  the  Labyrinthodon,  pictured  in 
Fig.  139  (p.  240).  Though  having  a  head  of  three  or  four 
feet  in  length,  and  teeth  three  inches  long,  and  being 
about  the  size  of  an  ox,  with  his  long  hind  legs,  he  was 
very  much  like  a  frog.  All  of  his  skeleton  has  never 
been  discovered,  but  from  his  skull  and  some  other  bones 
Professor  Owen,  by  his  knowledge  of  the  adaptation  of 
bones  to  each  other,  like  Cuvier,  has  reconstructed  in  his 
mind  the  whole  frame  of  the  animal,  and  the  result  is  the 
singular  form  which  you  have  in  the  figure.  The  tracks 
which  you  see  in  the  figure  have  been  observed  alone,  in 
Triassic  rocks,  and  have,  until  recently,  been  supposed 


Fig.  137. 


240 


GEOLOGY. 


Fig.  139. 

to  belong  to  another  animal,  whose  remains,  however, 
had  never  been  discovered.  The  name  of  Cheirotheri- 
um  was  given  to  this  supposed  animal  because  the  tracks 
were  so  much  like  the  print  of  a  hand,  the  word  being 
derived  from  two  Greek  words,  cheir,  hand,  and  therion, 
beast.  It  is  now  pretty  well  ascertained  that  these 
tracks  were  all  made  by  the  Labyrinthodon.  This  name 
is  given  to  this  animal  from  the  structure  of  its  teeth. 
In  Fig.  140,  at  a,  is  a  tooth  half  its  natural  size,  and  at  b 


Fig.  140. 

is  part  of  a  transverse  section  magnified  twenty  diame- 
ters. You  see  that  the  turnings  on  this  surface  have  a 
labyrinthine  arrangement,  and  hence  the  name  given  to 
the  animal.  At  c  is  one  of  these  turnings  very  highly 
magnified. 

346.  Tracks.  —  The  tracks  of  Triassic  animals  have 
been  observed  by  geologists  in  various  quarters,  but  most 
largely  by  Professor  Hitchcock,  of  this  country,  in  the 
red  sandstones  of  the  Connecticut  River  Valley,  where 


AGE   OF   REPTILES. 

they  abound.     Before  he  began 
his  observations  in  1835,  these 
tracks  had  been  noticed  for  full 
forty    years    by    persons    who 
were  not  aware  of  their  great 
geological  interest.     Some  are 
tracks  of  birds,  some  of  reptiles, 
and  some  of  animals  that  had  in 
combination  the  characteristics 
of  both  birds  and  reptiles — rep- 
tilian birds,  as  they  may  be  call- 
ed.    In  Fig.  141  is  represented 
a  slab  of  sandstone  found  near 
Mount    Holyoke.      The    large 
tracks    show   that  the    animal 
which  made  them  on  the  mud, 
now  hardened  into  rock,  had  a 
foot  20  inches  long  and 
21  wide.    It  is  supposed 
that   he    was   a   Batra- 
chian,  a  toad-like  animal, 
and  yet  he  must  have 
been  of  the  size  of  an  ele- 
phant. There  are  tracks, 
a  £,  of  some  smaller  ani- 
mal, and  much  of  the  sur- 
face shows  also  the  im- 
pressions  of  rain-drops 
as   distinctly  as  if  they 
were   made    yesterday. 
One  of  the  largest  of  the 
birds  of  that  period  was 
the  Brontozoum  gigan- 
teum,   whose    track    is 
given   in    Fig.  142    (p. 
242).   Its  feet  were  from 
14  to  20  inches  long,  its 
L 


241 


242 


Fig.  142. 

stride,  as  shown  by  the  tracks,  from  four  to  six  feet,  and 
it  is  supposed  that  it  reached  a  height  of  14  feet.  A 
very  singular  track  is  represented  in  Fig.  143.  An  im- 
pression like  a  brush  extends  back  from  the  foot.  It  is 
supposed  that  the  heel  was  covered  with  ridges,  which 
made  these  lines. 

347.  A  Stone  Fossil  Book. — A  book  with  stone  leaves 
has  been  deposited  by  Professor  Hitchcock  in  the  Am- 
herst  Ichnological  Cabinet.  It  is  a  book  of  five  leaves, 
nineteen  inches  long  by  eight  in  width,  each  leaf  being 
about  an  inch  thick.  The  impressions  of  the  tracks  of 
an  animal  are  on  all  the  leaves,  corresponding  in  position 


AGE    OF    REPTILES. 


243 


throughout.  The  explanation  is  this :  Five  successive 
layers  of  mud  had  been  laid  down  of  this  thickness,  each 
one  having  partly  dried  before  the  succeeding  one  was 
laid.  The  animal  treading  upon  the  upper  one  made  an 
impression  through  the  whole  five  layers,  which  after- 
ward solidified  into  rock,  and  so  were  preserved  through 
long  ages  to  the  present  time.  Dr.  Hitchcock  ingenious- 
ly mounted  the  leaves  in  such  a  way  that  the  book  can 
be  readily  opened  or  shut. 

348.  Trap  Rocks. — Masses  of  these  rocks  have  come 
up  among  the  Triassic  rocks  in  the  eastern  part  of  this 
country,  many  of  them  being  lofty  enough  to  be  called 
mountains.  As  examples  of  these,  there  are,  in  Massa- 
chusetts, Mounts  Tom  and  Holyoke ;  in  Connecticut, 
East  and  West  Rock  at  New  Haven,  and  the  Hanging 
Hills  of  Meriden  ;  in  New  Jersey,  Bergen  Hill,  and  vari- 
ous other  elevations.  I  have  already  told  you,  in  §  230, 
how  these  masses  are  formed.  The  effect  which  the 
fused  rock,  as  it  was  thrust  upward,  produced  upon  the 
sandstone  is  plainly  to  be  seen  in  many  localities.  The 
difference  between  the  sandstone  close  by  the  trap  and 
that  which  is  away  from  it  is  as  distinct  as  that  between 
a  brick  so  burned  as  to  be  very  hard  and  one  which  has 
the  ordinary  hardness.  The  ridges  and  dikes  of  trap  are 
arranged  with  some  system,  extending  in  certain  general 
directions  as  mountains  do.  This  may  be  seen  in  Perci- 


244 


GEOLOGY. 


val's  map  of  them  in  his  Geological  Survey  of  Connecti- 
cut. The  eruptions  of  trap  are  not  wholly  confined  to 
Triassic  rocks,  but  appear  to  some  extent  on  either  side 
of  the  area  occupied  by  them,  making  ridges  and  dikes 
among  the  other  rocks. 


Fig.  144. 

349.  Plants  of  the  Jurassic  Period.— The  climate  of  the 


AGE    OF    EEPTILES. 


245 


earth  was  quite  universally  warm  and  genial,  as  is  shown 
by  the  wide  diffusion  of  certain  plants  and  animals,  even 
into  the  arctic  regions.  The  vegetation,  therefore,  was 
luxuriant,  consisting  largely  of  cycads,  conifers,  and  tree- 
ferns,  with  some  palms,  lilies,  etc.  There  were  also  equi- 
setums  and  club-mosses.  In  Fig.  144  is  represented  the 
vegetation  of  this  period.  In  many  localities  the  luxuri- 
ant vegetation  was  packed  down  in  beds  of  coal,  as  in 
the  Carboniferous  period.  There  are  localities  of  this 
kind  in  Europe,  in  Great  Britain,  in  China,  in  India,  and 
in  Virginia  in  this  country.  Coal  can  be  made  of  vege- 
table fibre  at  any  period  if  those  circumstances  are  pres- 
ent which  I  have  stated  to  be  necessary  in  the  chapter 
on  the  Coal-making  age. 

350.  Portland  Dirt-bed. — In  the  island  of  Portland, 
and  in  some  of  the  adjoining  counties  of  England,  there 
have  been  found  the  remains  of  an  ancient  forest  of  the 
Oolitic,  or  Jurassic  period,  lying  between  the  strata. 
This  so-called  Portland  dirt-bed  is  composed  of  a  bluish 
loam,  which  contains  stumps  and  roots  of  trees  petrified, 
as  represented  in  Fig.  145.  There  are  strata  of  rock 


Fig.  145. 


above  and  below ;  those  below,  A,  being  mostly  marine 
limestone,  and  those  above,  C,  being,  on  the  other  hand, 
fresh-water  limestone.  The  rocky  strata  and  the  dirt- 
bed,  you  see,  are  all  parallel,  but  not  horizontal.  They 
were  horizontal  when  they  were  formed,  but  have  all  in 
some  way  been  tilted  up  together.  This  tilting,  howev- 
er, is  only  found  in  some  localities,  the  horizontal  posi- 


246  GEOLOGY. 

tion  being  retained  in  others.  Now,  in  all  the  region 
where  this  arrangement  is  found,  there  must  have  been, 
in  the  first  place,  deposits  of  a  marine  character,  for  the 
Portland  stone,  A,  is  filled  with  marine  shells.  After- 
ward these  beds  were  covered  with  lake  or  river  mud, 
which  became  dry  land,  and  was  the  scene  of  a  forest  veg- 
etation. Then  the  land  sank  down,  and  was  submerged, 
with  its  load  of  forest  growth,  beneath  fresh  water  in 
place  of  the  salt  water  which  was  there  before  the  dirt- 
bed  was  laid.  From  this  water  the  limestone  strata,  C, 
were  deposited  upon  the  dirt-bed,  B,  this  being  demon- 
strated by  the  shells  in  the  stone,  which  are  of  the  kinds 
that  are  found  only  in  fresh  water.  The  tilting,  which 
is  to  the  amount  of  45  degrees,  was  not  done  till  all  the 
fresh-water  limestones,  C,  were  laid  down. 

351.  Animals. — Animal  life  had  advanced  on  its  forms 
in  the  previous  age,  though  the  fishes  were  still  only  ga- 
noid and  placoid,  and  the  mammalia  were  still  of  the  mar- 
supial type.  Insects  appeared  more  largely  than  before, 
because  there  was  more  food  for  such  animals  in  the  veg- 
etation. "  There  were,"  says  Page,  "  burro wers  among 
the  decaying  timber  of  the  pine  forests;  leapers  among 
the  leaves  and  herbage  of  the  cycas  grove;  hunters  along 
the  river-bank  and  across  its  sunny  waters ;  and  gaudy 
flutterers  over  the  flowers  of  the  lily  and  the  palm-tree. 
All  the  great  orders  of  insect  life — beetles,  cockroaches, 
dragon-flies,  grasshoppers,  and  ants — are  abundantly  rep- 
resented." The  Crustaceans  were  numerous,  those  which 
were  similar  to  shrimps  and  lobsters  being  especially  prev- 
alent. The  higher  orders  of  Mollusks  abounded.  There 
were  still  Crinoids,  though  they  were  on  the  wane.  Cor- 
als were  abundant  wherever  the  formation  of  limestone 
was  going  on.  Sea-urchins  also  were  numerous,  one  of 
which  is  represented  in  Fig.  146.  But  the  reptilian  de- 
velopment was  the  great  feature  of  this  middle  portion  of 
the  age  of  Reptiles.  There  were  reptiles  for  the  ocean, 
the  river  and  estuary,  the  muddy  shore,  and  the  land  ; 


AGE    OF    REPTILES. 


247 


and  many  of  them,  were 
monstrous  in  size  and 
extraordinary  in  char- 
acter. 

352.  Ammonites  and 
Belemnites.  —  Of  the 
Mollusks,  these  are  the 
most  prominent  and 

They  belong  to  the  class  called  Cephalopods 
(§  286).  The  Ammonites,  which  began  in  the  Triassic 
period,  were  now  very  abundant,  their  beautiful  shells 


peculiar. 


^~^  -—sff^-'"'^^™  '^^  i 


1.  Ammonite!?  Jason.    2.  A.  Communis.     3    A.  Bucklandi.     4,  5, 6.  Belemnites. 
7.  Belemnoteuthis. 

Fig.  147. 

appearing  in  hundreds  of  forms,  with  every  variety  of 


248  GEOLOGY. 

ornamentation.  It  was  now  the  "  reign  of  the  Ammon- 
ites ;"  but  they  have  long  ago  passed  away,  and  the 
only  present  representative  of  the  class  is  the  Nautilus 
of  the  Southern  Ocean.  Some  of  these  ancient  Am- 
monites were  monsters,  being  even  three  feet  in  diame- 
ter. On  the  left  of  Fig.  147  (p.  247)  are  three  species. 
On  the  right  of  the  figure  are  the  Belemnites,  in  different 
degrees  of  preservation.  These  belong  to  the  Cuttle-fish 
tribe.  At  7  is  one  with  its  crown  of  arms,  with  which 
it  took  its  prey.  The  animal  probably  sailed  along  with 
its  long,  conical  shell  pointed  downward,  and  now  and 
then  rose  quickly  to  grasp  some  fish  swimming  above  it, 
darting  down  to  the  bottom  to  devour  it.  Like  the  cut- 
tle-fish of  the  present  day,  the  Belemnite  had  an  ink-bag, 
and  used  it  for  the  same  purpose — to  discolor  the  water 
to  aid  it  in  escaping  from  its  enemies.  From  the  ink- 
bag  of  a  Belemnite  found  at  Lyme  Regis,  in  England,  a 
pigment  was  obtained  like  that  which  is  now  prepared 
from  the  cuttle-fish  under  the  name  of  India  ink. 

353.  Ichthyosaurus. — This  animal,  whose  skeleton  is 
represented  in  Fig.  148,  combined  in  itself  the  character- 


Fig.  148. 

istics  of  a  porpoise,  a  fish,  and  a  crocodile.  Its  large 
head  was  pointed  like  that  of  a  porpoise,  and  it  had  pad- 
dles or  flippers  like  the  Porpoise  family.  It  was  like  a 
fish  in  having  no  neck,  the  head  and  body  being  contin- 
uous in  outline.  It  was  also  like  a  fish  in  the  arrange- 
ment of  its  spinal  column.  Its  teeth  and  jaws  were  like 
those  of  a  crocodile.  Its  eye  was  very  large,  its  socket 
being  eighteen  inches  in  diameter.  It  was  so  construct- 
ed that  the  animal  could  see  equally  well  in  and  out  of 
the  water.  Its  jaws  were  so  long  that,  when  fully  open- 
ed, their  extremities  would  be  seven  feet  apart.  It  was, 


AGE    OF   REPTILES. 


249 


in  some  cases,  even  thirty  feet  in  length.  One  of  its  pad- 
dles contained  over  a  hundred  bones,  giving  this  instru- 
ment great  elasticity  and  power.  Thirty  species  of  this 
animal  have  been  discovered. 

354.  Flesiosauras.— This  animal,  of  which  you  see  the 
skeleton  represented  in  Fig.  149,  had  the  general  plan  of 


Fig.  149. 


the  Ichthyosaurus,  but  differed  from  it  in  several  mate- 
rial particulars)  It  was  fitted  for  more  brisk  motion. 
Its  head  was  flat  and  serpent-like.  It  had  a  very  long 
neck,  its  paddles  were  large  but  slender,  and  its  tail 
short.  In  swimming,  it  probably  used  its  paddles  more 
and  its  tail  less  than  the  Ichthyosaurus.  The  greatest 
difference,  hpwever,  is  in  the  size  of  the  head.  The 
length  of  the  Plesiosaurus  was  about  17  feet.  Both  ani- 
mals had  the  power  of  creeping  on  land. 

355.  Pterodactylus. — The  Pterodactyl  is  the  most  ex- 
traordinary of  the  animals  of  this  period.  It  had  the 
head  and  neck  of  a  bird,  the  mouth  of  a  crocodile,  the 


250  GEOLOGY. 

wings  of  a  bat,  and  the  body  and  tail  of  a  mammal.  It 
was,  in  some  cases,  of  such  enormous  size  that  it  meas- 
ured from  tip  to  tip  of  the  spread  wings  18  or  20  feet. 
Although  the  general  appearance  of  its  wings  was  like 
the  bat,  the  arrangement  was  different.  Instead  of  four 
extended  toes  enveloped  in  skin,  as  in  the  bat,  the  fifth 
toes  only  were  lengthened,  and  the  skin  extended  along 
the  side  of  the  body  and  legs.  Its  eyes  were  enormously 
large,  so  that  it  probably  could  seek  its  prey  in  the  night. 
In  Fig.  150  (p.  249)  you  see  the  skeleton  as  it  was  found 
in  one  case,  and  in  Fig.  151  it  is  represented  as  complete 


Fig.  151. 

and  in  order,  so  that  you  see  the  relative  position  and 
size  of  the  various  parts. 

356.  A  Question  in  Comparative  Anatomy. — In  Fig. 
152  we  have  the  Ichthyosaurus,  Plesiosaurus,  and  Pter- 
odactyl as  they  are"  supposed  to  have  appeared  in  the 
scenes  of  the  Jurassic  age.  It  has  been  commonly  sup- 


AGE    OF    REPTILES. 


posed  that  the  Pterodactyl  was  a  flying  animal,  as  here 
represented,  and  that  it  lived  on  insects  as  the  bats  do, 
although,  perhaps,  at  the  same  time,  it  would  dive  down 
occasionally  into  the  water  for  fishes,  to  mingle  them 
with  its  insect  food.  Agassiz  expresses,  on  the  contra- 
ry, the  opinion  that  it  was  an  aquatic  animal,  preying 
upon  fish  and  other  animals  in  the  water.  This  opinion 
he  bases  upon  two  facts.  First,  the  teeth  are  conical, 
sharp,  and  separated  from  each  other,  and  are,  indeed, 
such  as  are  common  to  animals  that  live  on  aquatic  prey, 
and  such  as  would  not  be  required  for  the  capture  and 
destruction  of  insects.  Secondly,  there  is  nothing  in  the 
frame-work  of  the  breast  of  the  animal  to  indicate  that 


252 


GEOLOGY. 


it  had  those  powerful  muscles  which  flying  animals  al- 
ways have.  Instead  of  the  projecting  keel  which  birds 
have  for  the  attachment  of  their  large  flying  muscles,  it 
has  a  thin,  flat  breast-bone,  like  that  of  the  sea-turtle  of 
the  present  day.  For  the  full  exposition  of  the  subject 
of  arrangements  for  flying,  I  refer  you  to  my  Natural 
History,  §§199  and  200.  It  may  be  added  to  the  rea- 
sons which  Agassiz  has  given  for  his  opinion  that  there 
were,  so  far  as  we  know,  no  insects  of  sufficient  size  to 
be  food  for  so  large  an  animal.  But,  after  all,  there  was 
in  the  Pterodactyl  an  apparatus  which  might  be  used,  to 
some  extent,  in  flying,  though  there  were  no  muscles 
competent  to  sustain  flight  for  any  length  of  time.  "We 
must  therefore  conclude  that  it  probably  rose  into  the 
air  occasionally,  very  much  as  the  flying-fish  now  does, 
with,  perhaps,  a  somewhat  longer  range  of  flight. 

357.  Dinosaurs. — There  is  a  class  of  Jurassic  land  rep- 
tiles called  Dinosaurs,  the  name  coming  from  two  Greek 
works,  deinos,  terrible,  and  sauros,  lizard.  Two  of  these, 
Megalosaur  and  Hyla3osaur,  are  represented  in  Fig.  153. 


Fig.  153. 


Another  is  the  Iguanodon,  so  called  because  it  was  like 
the  Iguana  family  of  the  present  day,  a  notice  of  which 


AGE    OF    EEPTILES.  253 

you  will  find  in  my  Natural  History,  §  326.  These  mon- 
strous animals,  being  25  or  30  feet  in  length,  roamed,  el- 
ephant-like, over  the  river  plains  or  through  the  forests, 
the  Iguanodon  browsing  upon  shrubs  and  trees,  and  the 
Megalosaur  and  Hylseosaur  devouring  crocodiles  and 
tortoises. 

358.  Cretaceous  System. — In  Europe  and  Asia  the  se- 
ries of  rocks  belonging  to  this  system  is  characterized  by 
the  presence  of  sands  and  sandstones  in  the  lower  part, 
and  chalk  in  the  upper  part.     In  this  country  there  is  no 
chalk  in  the  series,  but  there  are  beds  of  sand,  clay,  marl, 
and  different  kinds  of  limestone.    Sandy  strata  of  various 
kinds  and  colors  predominate.     Some  are  solid,  and  oth- 
ers are  more  or  less  loose  in  their  structure — some  so 
much  so  that  they  can  be  crumbled  by  the  hand.     There 
is  a  dark  green  variety  called  the  Green-san^  the  great- 
est part  of  which,  sometimes  even  to  90  per  cent.,  is  sili- 
cate of  iron  and  potash.     There  is  also  a  little  phosphate 
of  lime  in  it.     It  is  prized  as  a  fertilizer  in  New  Jersey 
and  other  parts  of  this  country,  its  virtue  in  this  respect 
coming  from  the  potash  and  the  phosphate.     In  England 
the  Green-sand  gives  its  name  to  the  whole  of  the  lower 
part  of  the  Cretaceous  series,  because  it  is  so  prominent 
in  it.     Chalk,  which  is  so  prominent  a  part  of  the  series 
in  England  and  Europe,  is,  like  limestone  and  marble,  a 
carbonate  of  lime,  but  loosely  put  together  in  compari- 
son with  them.     The  chalk  is  varied  in  character  by  the 
different  kinds  of  impurities  that  are  apt  to  be  mingled 
with  it,  and  their  different  proportions. 

359.  Localities. — In  this  country  the  Cretaceous  sys- 
tem comes  to  the  surface  over  a  vastly  larger  area  than 
the  other  two  series  of  Mesozoic  rocks,  the  Triassic  and 
Jurassic.     It,  in  fact,  made  a  very  large  addition  to  the 
North  American  continent  in  the  west  and  southwest, 
chiefly  west  of  the  Mississippi,  though  quite  largely  in 
the  states  bordering  on  the  Gulf  of  Mexico.     In  the  east 
it  appears  here  and  there  from  New  Jersey  down  to 


254  GEOLOGY. 

South  Carolina.  It  is  very  prominent  in  England,  the 
famous  Dover  Cliffs  being  composed  of  the  chalk,  and  it 
appears  on  the  other  side  of  the  Channel,  in  France.  It 
also  shows  itself  in  other  portions  of  France,  and  in  vari- 
ous parts  of  Europe. 

360.  Source  of  the  Chalk. — Chalk  is  a  marine  deposit, 
and  it  is  supposed  that  it  was  made  in  water  some  two 
or  three  hundred  feet  deep.      It  was  made  chiefly  by 
those  minute  animals  called  Foraminifera,  the  shells  of 
some  of  whose  species  are  represented  in  Fig.  83,  p.  157. 
The  evidence  on  this  point  is  decisive.    The  observations 
of  Ehrenberg  and  others  with  the  microscope  show  that 
chalk  is  made  up  of  shells,  the  foraminifera  furnishing  by 
far  the  largest  proportion  of  them.     Ehrenberg  states 
that  a  cubic  inch  of  chalk  often  contains  over  a  million 
of  these  microscopic  organisms.     Whenever  you  make 
a  mark  with  chalk  upon  the  blackboard,  you  really  de- 
posit there  a  quantity  of  the  shells  of  these  organisms ; 
and  if  your  eyes  could  be  suddenly  endowed  with  a  high 
magnifying  power,  that  white  line  would  appear  to  you 
like  part  of  the  wall  of  a  grotto  covered  over  with  shells. 
Indeed,  the  fact  that  the  carbonate  of  lime  has  in  any 
case  the  form  of  chalk  is  owing  to  the  aggregation  of 
these  shells,  they  being  so  small  that  they  give  to  the 
rock  formed  from  them  a  soft  and  porous  character. 
This  character  is  not  given  to  the  rock  under  any  ordi- 
nary circumstances  when  it  is  formed  from  corals  or 
shells  of  any  size.     These  same  foraminifera  are  busy  at 
the  present  day  taking  from  the  water  of  the  ocean  car- 
bonate of  lime  to  form  their  shells,  and  these,  being  left 
on  the  sea's  bottom,  have  been  found  in  some  localities 
to  compose  almost  wholly  the  sand  that  has  been  brought 
up  in  deep  soundings.     The  material  for  chalk  is  then 
being  deposited,  and  the  chalk  wrhich  may  thus  be  made 
may  at  some  future  period  be  raised  to  the  surface,  and 
constitute  a  part  of  the  dry  land  of  our  earth. 

361 .  Flint  in  the  Chalk. — In  England,  and  other  coun- 


AGE    OF    REPTILES. 


255 


tries  where  chalfc  abounds,  flint  is  found  in  it  to  a  con- 
siderable depth.  Sometimes  it  appears  in  layers,  but 
commonly  in  nodules  or  lumps,  of  various  sizes  and 
shapes.  The  nodules  are  sometimes  irregular  and  gro- 
tesque, and  when  so  are  quite  a  favorite  ornament  in  cot- 
tage gardens  in  England.  Covered  with  whitewash, 
they  are  used  as  edges  to  the  borders.  One  of  these 
forms  you  see  in  Fig.  154.  Sometimes  these  nodules 


Fig.  154. 

take  such  a  form  as  to  be  called  fossil  mushrooms.  In 
such  cases  the  flint  was  depos- 
ited upon  and  in  certain  com- 
pound polypes  of  these  forms, 
or,  in  other  words,  they  are  pet- 
rifactions of  the  frame-work  of 
these  animals.  Two  of  these  are 
seen  in  Fig.  155.  Such  forms 
are  called  Ventriculites. 
362.  Fossils  in  the  Flint. — There  are  some  very  inter- 
esting minute  fossils  in  the  flint  nodules.  Some  of  these 
I  will  notice.  There  are  certain  vegetable  fossils  called 
Xanthidia,  which,  like  the  diatoms,  were  formerly  sup- 
posed to  be  animal.  There  are  many  species  of  them. 
In  Fig.  156  (p.  256),  at  2,  you  see  represented  a  chip  of 
flint,  which  is  so  thin  that  the  Xanthidia  can  be  seen  by 
transmitted  light.  The  five  spots  mark  the  frame-works 
of  five  of  them.  The  figure  below  exhibits  one  of  these 


Fig.  155. 


256 


GEOLOGY. 


Fig.  156. 


largely  magnified.  It  is  supposed  that 
each  of  them  furnished  a  nucleus  around 
which  the  flint,  dissolved  in  the  water 
of  the  ocean,  gathered  and  solidified. 
In  the  upper  part  of  Fig.  157,  at  a,  c, 
and  $,  are  shell  prisms  that  are  found 
in  flint,  those  at  a  being  the  most  com- 
mon form.  They  are  magnified  ten 
times,  as  indicated.*  The  origin  of 
these  prisms,  which  are  composed  of 
carbonate  of  lime,  is  curious.  They 
come  from  the  shells  of  certain  bi- 
valves of  that  period.  Now  shells  are 
ordinarily  made  with  laminaB  or  layers,  one  placed  upon 
another,  as  you  may  see  in  an  oyster.  But  the  shells  of 
these  strange  bivalves  are  composed  of  prisms,  or  many- 
sided  columns  packed  together,  and  extending  from  the 
inside  to  the  outside.  In  the  figure,  at  5,  we  have  a 
piece  of  flint,  with  a  piece  of  one  of  these  shells  imbed- 
ded in  it.  Some  of  the  shell  has  been  dissolved  and  re- 
moved, so  that  you  see  in  the  recess  the  little  columns 
standing  up  all  around,  and  on  the  floor  of  the  cavity 
are  the  minute  depressions  in  the  flint  made  by  their 
ends.  In  the  specimen  of  which  this  figure  is  a  repre- 
sentation there  was  a  roof  of  flint  over  the  recess,  but 
this  was  carefully  ground  off  in  order  to  show  the  ar- 
rangement. In  the  lower  part  of  the  figure  you  see  rep- 
resented a  great  variety  of  flinty  spicula  which  come 
from  sponges,  and  are  found  in  the  flint  nodules.  They 
are  all  much  magnified,  one  of  them,  £,  even  a  hundred 
times.  This  is  very  rarely  found.  The  most  common 
of  these  spicules  are  #,  A,  &,  and  p.  The  spindle-shaped 
one,  with  raised  rings,  o,  is  by  no  means  uncommon. 
The  one  resembling  it,  but  having  a  triradiate  summit, 

*  Throughout  Fig.  157  the  character  X  means  multiplied  or  mag- 
nified, the  numeral  annexed  showing  to  what  degree  the  object  is 
magnified. 


AGE    OF    REPTILES. 


257 


Fig.  157. 


n,  occurs  more  rarely.  At  m  is  the  form  which  prevails 
in  patches  of  silicious  network.  It  is  supposed  that  the 
spicula  of  sponges  and  the  shells  of  the  little  diatoms 


258  GEOLOGY. 

furnished  a  large  portion  of  the  flint  for  the  nodules  in 
the  chalk.  The  sponges  abounded  at  that  period,  and 
had  an  agency  in  regard  to  silicious  matter  similar  to 
that  which  corals  have  had  in  relation  to  limestone,  and, 
to  some  extent  at  least,  they  have  that  agency  still. 

363.  Animals  of  the  Cretaceous  Period.  —  I  have   al- 
ready spoken  of  the  Foraminifera  and  the  Sponges.    The 
corals  were  not  so  abundant  as  in  the  Jurassic  period. 
The  sea-urchins  were  very  numerous,  and  the  preserva- 
tion of  their  beautiful  remains  is  one  of  the  marked  fea- 
tures of  the  period  of  the  Chalk.     The  Crinoids,  or  En- 
crinites,  were  decidedly  on  the  wane.     The  Crustaceans 
were  on  the  increase,  and  approached  in  character  to  the 
crabs  and  lobsters  of  the  present  day.     The  fishes  ex- 
hibited a  great  change.     Though  some  of  the  placoids 
and  ganoids  of  former  ages  still  remained,  the  ctenoids 
and  cycloids,  which  are  now  the  prevailing  orders,  first 
appeared  in  the  Cretaceous  age.     The  great  reptiles  of 
the  Jurassic  period  were  passing  away,  for  this  was  the 
concluding  period  of  the  Reptilian   age.     The  higher 
mollusks  appeared  in  great  profusion.     There  was  a  re- 
markable change  in  the  forms  of  that  great  tribe  of  mol- 
lusks, the  Ammonites.    Before  this  the  coil  of  their  cham- 
bered cells  was  close  and  on  one  plane,  as  seen  in  Fig. 
147 ;  but  now  the  coil  was  more  or  less  open  in  many 
of  the  species,  sometimes  with  fantastic  variations,  or  it 
was  spiral.     Examples  are  given  in  Fig.  158,  where  we 
have,  1.  Ancyloceras,  incurved  like  a  crosier.     2.  Scaph- 
ites,  curved  like  the  prow  of  a  skiff.    3.  Crioceras^  curled 
like  a  ram's-horn.     4.  Hamites,  bent  like  a  hook ;  and,  5, 
Turrilites,  running  in  a  spiral  round  a  straight  axis. 

364.  Uplifts  at  the  Close  of  the  Reptilian  Age.— While 
there  were  some  disturbances  during  the  progress  of  this 
age,  there  were  great  and  extensive  ones  at  its  close,  in 
the  interval  of  passage  from  Mesozoic  to  Cainozoic  time, 
just  as  there  were  at  the  close  of  Paleozoic  time,  as  no- 
ticed in  §  337.     Some  of  the  great  chains  of  mountains 


AGE    OF    REPTILES. 


L>59 


Fig.  158. 


rose  into  existence  in  this  interval — the  Rocky  Mount- 
ains, the  Andes,  portions  of  the  Alps,  etc.  The  same  up- 
lifting continued  into  the  next  age,  so  that  these  mount- 
ains, and  the  Himalayas,  Pyrenees,  Appenines,  etc.,  were 
then  fully  raised.  The  evidence  in  regard  to  the  rising 
of  mountains  during  both  these  periods  is  twofold.  1st. 
The  rocks  of  the  cretaceous  system  lie  high  up  on  their 
sides ;  2d.  The  marine  rocks  of  the  tertiary  system — that 
is,  of  the  age  of  Mammals,  flank  their  sides  below  at  a 
different  slope.  Take,  for  example,  the  Rocky  Mount- 
ains. The  cretaceous  rocks  are  found  lying  sloped  high 
up  upon  them.  This  proves  that  the  sea,  from  whose 
waters  the  materials  of  the  cretaceous  rocks  were  depos- 
ited, stood  over  the  region  where  these  mountains  now 
are,  and  that  these  rocks  were  raised  up  after  the  Creta- 
ceous age  had  passed.  Then  the  tertiary  rocks  were  de- 
posited from  waters  which  flowed  about  the  base  of  the 
mountains.  But  how  do  we  know  that  the  raising  of 
them  was  not  completed  till  some  time  in  the  Tertiary 
age  ?  If  it  was  completed,  the  rocks  of  the  tertiary  sys- 
tem would,  of  course,  not  be  sloped  up  the  sides  of  the 


260  GEOLOGY. 

mountains  at  all ;  but  if  it  was  not,  they  would  be  thus 
sloped  in  proportion  to  the  degree  of  raising  in  the  ter- 
tiary, and  such  sloping  is  actually  found  to  exist.  All 
this  is  simply  an  illustration  of  what  is  explained  with 
figures  in  §  226.  In  this  uplifting  of  strata  in  the  forma- 
tion of  mountains,  remains  of  animals  which  once  lived 
in  the  sea  have  been  raised  to  very  great  heights.  They 
have  been  found  imbedded  in  the  strata  in  the  Alps  at 
the  height  of  six  or  eight  thousand  feet,  and  in  the  An- 
des, according  to  Humboldt,  at  the  height  of  fourteen 
thousand  feet — that  is,  over  two  miles  and  a  half. 

365.  Destruction  of  Life  at  the  End  of  this  Age. — As  at 
the  end  of  Palaeozoic  time  (§  338),  so  now  at  the  end  of 
Mesozoic  time,  there  was  nearly,  if  not  quite,  a  universal 
destruction  of  life.     In  both  cases  this  was  owing  to  the 
great  disturbances  that  occurred.     It  is  supposed  that 
after  the  Cretaceous  period  was  completed,  in  the  move- 
ment which  raised  the  mountains,  of  which  I  have  spoken 
in  §  364,  there  was  a  general  elevation  of  the  land  of  the 
northern  regions,  and  that  the  severe  cold  which  was 
thus  produced  was  at  least  a  prominent  agency  in  the 
destruction  of  life  at  this  period.     Hugh  Miller  makes 
these  two  gaps  or  breaks  the  basis  of  a  division  of  the 
life  of  the  world  into  three  dynasties :  the  dynasty  of  the 
Fish,  extending  from  the  Azoic  age  to  the  end  of  Palae- 
ozoic time,  when  the  first  break  occurs ;  the  dynasty  of 
the  Reptile,  from  this  period  to  the  end  of  Mesozoic  time, 
when  the  second  break  occurs ;  and  the  last,  the  dynas- 
ty of  the  Mammal,  which,  commencing  after  the  second 
break,  continues  at  the  present  time. 

366.  New  Creations. — During  all  the  progress  of  the 
ages,  whenever  a  new  species  of  plant  or  animal  ap- 
peared, there  was  a  new  creation,  as  already  intimated 
in  §  273.     And  as  the  life-record  of  the  rocks  shows  that 
there  have  been  continually  extinctions  of  species,  and 
introductions  of  new  species  in  their  places,  creative  pow- 
er has  been  continually  exerted  in  the  domain  of  life  upon 


AGE    OF    MAMMALS.  261 

our  earth.  But  this  power  was  specially  active  when, 
in  the  great  and  extensive  changes  effected  at  times  in 
the  earth's  crust,  as  was  often  the  case,  life  was  largely 
destroyed.  And  when  the  destruction  was  complete  in 
the  two  gaps  that  have  been  mentioned,  there  succeeded 
an  entirely  new  creation  of  plants  and  animals. 


CHAPTER  XVIII. 

AGE     OF     MAMMALS. 

36V.  Transition  from  Mesozoic  to  Cainozoic  Time. — 
We  now  come  to  a  period  in  the  earth's  history  in  which 
there  is  a  decided  resemblance  to  the  present  time  in 
the  general  surface  of  the  earth,  and  in  its  vegetables 
and  animals.  The  surface  had  become  diversified  with 
numerous  mountains,  valleys,  and  rivers,  though  by  no 
means  as  largely  as  now,  for  this  diversification  was  com- 
pleted only  when  man  was  to  be  ushered  upon  the  scene. 
The  endogens  and  exogens,  the  great  sources  of  food  for 
man  and  beast,  were  quite  predominant  in  the  vegeta- 
tion of  the  earth.  In  the  animal  kingdom,  the  marsupi- 
als, which  are  allied  at  the  same  time  to  reptiles  and  to 
birds,  gave  way  to  mammalia  of  the  higher  orders.  In 
the  previous  ages  the  most  striking  displays  of  animal 
life  were  mostly  in  the  ocean,  in  huge  fishes,  and  mol- 
lusks,  and  reptiles ;  but  now  the  land  was  to  surpass  the 
sea  in  this  respect. 

368.  Divisions  of  Cainozoic  Time. — A  common  division 
of  the  Cainozoic  age  is  into  the  Tertiary  and  Post-terti- 
ary— the  Tertiary  occupying  the  time,  up  to  the  Glacial 
period,  when,  as  you  will  see,  the  agency  of  ice  was  ap- 
plied over  a  large  portion  of  the  earth  to  produce  im- 
portant results,  and  the  Post-tertiary,  extending  thence 
on  to  the  advent  of  man.  The  term  tertiary  is  an  old 
geological  term,  which  the  progress  of  discovery  has 
shown  to  be  inapplicable.  It  was  adopted  when  it  was 


262  GEOLOGY. 

supposed  that  the  crystalline  rocks  were  the  first  form- 
ed in  all  cases,  which  were  therefore  called  primary,  or 
primitive,  the  secondary  being  those  which  were  be- 
tween the  primary  and  tertiary  in  relative  age.  But 
when  it  was  found  that  the  so-called  primary  rocks  were 
formed  in  various  ages,  some  of  them  quite  recently,  this 
classification  was  given  up ;  but  the  name  tertiary  has 
been  retained,  by  common  consent,  as  a  matter  of  con- 
venience. Indeed,  the  three  terms  are  used  still  to  some 
extent,  as  mentioned  in  §  261,  primary  having,  however, 
a  different  meaning  attached  to  it  from  what  it  had  for- 
merly, it  being  applied  to  the  palaeozoic  rocks  instead  of 
those  which  are  originally  crystalline.  Lyell  has  divided 
the  strata  of  the  Tertiary  age  into  three  series,  according 
to  the  percentage  of  shells  found  that  are  the  same  with 
those  that  exist  now.  1.  Eocene,  the  term  being  derived 
from  two  Greek  words,  eos,  dawn,  and  Jcainos^  recent. 
When  the  name  was  adopted  it  was  supposed  that  from 
five  to  ten  per  cent,  of  the  species  found  in  the  strata 
were  identical  with  species  found  at  the  present  time, 
and  therefore  the  period  in  which  these  strata  were 
formed  was  very  properly  considered  as  the  dawn  of  the 
present  life  of  the  earth.  But  Dana  states  that  it  has 
been  discovered  that  the  species  of  this  period  are  all 
extinct.  2.  Miocene,  the  term  coming  from  meion,  less, 
and  Jcainos.  Here  from  ten  to  forty  per  cent,  of  the  spe- 
cies found  are  living  species  at  the  present  time.  3.  Pli- 
ocene, from  pleion,  more,  and  Jcainos.  Here  the  percent- 
age of  living  species  is  greater  than  in  the  miocene,  it 
being  from  fifty  to  ninety  per  cent.  These  three  series 
are  often  called  ancient  tertiary,  middle  tertiary,  and 
modern  tertiary. 

369.  Tertiary  Deposits. — In  the  previous  ages  the  stra- 
ta of  rocks  were  mostly  marine — that  is,  deposited  from 
the  waters  of  the  sea  as  sediment,  or  laid  down  by  coral 
and  other  animals  that  lived  in  the  sea.  But  now  many 
of  the  strata  were  either  lacustrine — that  is,  deposited 


AGE    OF    MAMMALS.  263 

in  lake  bottoms ;  or  estuary — that  is,  deposited  from  the 
waters  of  a  branch  of  the  sea,  where  there  was  a  min- 
gling of  salt  and  fresh  waters.  Some  deposits  occurred 
in  interior  (mediterranean)  seas.  There  was,  during  a 
part  of  the  Tertiary  age,  such  a  sea  in  Europe  of  immense 
extent,  with  vast  irregular  islands  in  it.  There  was  oft- 
en in  this  age  an  alternation  of  marine  and  fresh-water 
deposits,  as  shown  by  the  fossils  found  in  the  strata. 
This  is  the  case  with  the  basin,  so  called,  in  which  the 
city  of  Paris  lies.  First  in  order  we  have  plastic  clay,  a 
fresh-water  deposit.  Then  upon  this  are  strata  in  which 
there  is  a  vast  quantity  of  marine  shells.  This  is  the  cal- 
caire  grossier,  which  is,  for  the  most  part,  a  granular  yel- 
lowish limestone.  It  is  regularly  bedded  and  jointed,  so 
that  it  is  easy  to  quarry  it,  and  it  is  the  grand  building- 
stone  of  Paris.  Over  500  species  of  marine  shells  have 
been  discovered  in  these  strata.  By  some  changes  of 
the  land  in  some  way,  there  was  at  length  fresh  water 
over  all  that  region,  and  in  the  deposits  made  from  it 
upon  the  calcaire  grassier  there  are,  accordingly,  found 
remains  of  fresh-water  animals  and  plants.  Again  the 
sea  water  was  let  in,  and  we  have  a  marine  group  of 
strata,  to  be  followed  again  by  fresh  water  and  its  char- 
acteristic deposits.  In  these  last  fresh-water  beds  the 
most  peculiar  rock  is  the  millstone,  a  flinty  rock  full  of 
cells  and  winding  cavities,  occasioned,  it  is  supposed,  by 
the  escape  of  gas  from  the  bed  of  the  lake  up  through 
the  deposit  while  it  was  hardening. 

370.  Areas  of  the  Deposits. — The  deposits  of  strata  in 
this  age  were  not  made  over  areas  of  almost  continental 
extent,  as  was  the  case  in  the  previous  periods.  There 
were  elevations  of  land  here  and  there  over  the  spaces 
now  occupied  by  the  continents,  of  such  size  and  arrange- 
ment that  there  were  lakes,  and  estuaries,  and  inland  seas, 
and  on  the  floors  and  shores  of  these  the  deposits  were 
made.  As  these  elevations  multiplied  and  increased  dur- 
ing the  progress  of  the  age,  the  areas  of  deposition  were 


264  GEOLOGY. 

less  in  extent  in  the  latter  than  in  the  first  part  of  the 
age.  The  more  the  areas  became  divided,  the  more  di- 
versified and  complicated  were  the  deposits. 

371.  Tertiary  Rocks.— Most  of  the  rocks  of  this  age  are 
less  firm  than  those  of  previous  ages,  but  some  of  them 
are  very  hard.     They  are,  shell-rocks  of  various  kinds, 
shell-beds,  or  mixtures  of  shells  and  earth,  sandstones, 
marls,  clays,  beds  of  sand,  compact  limestones,  conglom- 
erates, buhrstones,  etc.     The  lowest  of  the  tertiary  rocks 
in  Europe  were  made  to  a  large  extent  from  materials 
derived  from  the  denudation  of  the  chalk  formation. 
For  this  purpose,  the  cretaceous  strata  were  upheaved 
from  the  sea  in  which  they  were  formed,  so  that  the  de- 
nuding water  could  act  upon  the  chalk  cliffs.     A  slow 
process  it  was  for  the  water  to  wear  away  sufficient 
amounts  of  these  emerged  strata  to  form  the  lower  ter- 
tiary strata  of  Europe,  and  a  long  age  was  required  to 
do  it. 

372.  Nummulitic  Formation. — I  have  already  noticed 
in  §  239  those  small  shell-animals  of  the  tribe  Foramin- 
ifera,  the  shells  of  which  have  formed  such  immense 
quantities  of  rocky  strata  in  Europe,  and  Asia,  and  Afri- 
ca.   In  Fig.  159,  at  1  and  2,  are  representations  of  nurn- 


Fig.  159. 

mulites  as  they  are  found  in  the  rocks,  and  at  3  is  a  sec- 
tion of  one,  showing  its  cells.  The  resemblance  of  these 
fossils  to  pieces  of  money  has  given  occasion  to  many  su- 
perstitious legends  in  regard  to  them  among  the  Ger- 
mans, and  they  are  very  commonly  called  the  devil's 


AGE    OF   MAMMALS.  265 

money.  The  nummulites  of  different  beds  are  of  differ- 
ent species  and  of  various  sizes,  some  of  them  reaching 
the  size  of  an  inch  and  a  half  in  diameter.  There  are, 
of  course,  other  shells  mingled  with  the  nummulites, 
though  some  strata  are  almost  entirely  nummulitic. 
"  The  nummulitic  formation,"  says  Lyell,  "  with  its  char- 
acteristic fossils,  plays  a  far  more  conspicuous  part  than 
any  other  tertiary  group  in  the  solid  frame-work  of  the 
earth's  crust,  whether  in  Europe,  Asia,  or  Africa.  It  oft- 
en attains  a  thickness  of  many  thousand  feet,  and  extends 
from  the  Alps  to  the  Carpathians,  and  is  in  full  force  in 
the  north  of  Africa,  as,  for  example,  in  Algeria  and  Mo- 
rocco. It  has  also  been  traced  from  Egypt,  where  it  was 
largely  quarried  of  old  for  the  building  of  the  Pyramids, 
into  Asia  Minor,  and  across  Persia  by  Bagdad  to  the 
mouths  of  the  Indus.  It  occurs  not  only  in  Cutch,  but 
in  the  mountain  ranges  which  separate  Scinde  from  Per- 
sia, and  which  form  the  passes  leading  to  Caboul ;  and  it 
has  been  followed  still  farther  eastward  into  India,  as  far 
as  eastern  Bengal  and  the  frontiers  of  China."  In  the 
Swiss  Alps  nummulitic  strata  are  found  10,000  feet  above 
the  level  of  the  sea,  and  in  Thibet  at  the  height  of  16,500 
feet.  They  enter  into  the  composition  of  the  central  and 
loftiest  parts  not  only  of  these  mountains,  but  of  the  Py- 
renees, the  Carpathians,  and  Himalayas.  Where,  there- 
fore, these  great  mountain  chains  now  are,  the  sea  stood 
during  that  long  age,  when  those  little  animals,  the 
nummulites,  were  accumulating  these  vast  masses  of 
rock  to  be  raised  in  after  ages  into  lofty  mountains  by 
some  of  the  processes  noticed  in  §  226.  Though  there 
are  some  nummulites  found  in  the  strata  of  the  same  pe- 
riod in  this  country,  they  did  not  play  here  the  magnifi- 
cent role  in  rock-making  which  they  did  in  Europe,  Asia, 
and  Africa. 

373.  Tertiary  Plants. — In  the  earlier  parts  of  the  Ter- 
tiary period  the  climate  of  the  earth  was  more  uniform- 
ly mild  than  in  the  latter,  and  therefore  in  the  strata  of 

M 


266  GEOLOGY. 

that  time  we  find  in  the  northern  portions  of  the  earth 
the  remains  of  such  plants  as  would  naturally  flourish  in 
warm  climates.  There  are  palm-like  leaves  and  fruits, 
leguminous  seeds  of  arboreal  growth,  twigs  arid  leaves 
of  mimosa,  laurel,  and  other  plants,  all  allied  to  what 
now  grow  in  southern  latitudes,  and  quite  in  contrast 
with  the  plants  now  found  in  the  same  localities.  Asso- 
ciated with  the  twigs,  leaves,  and  fruits  found  in  the 
strata  are  beds  of  lignite,  or  brown  coal,  indicating  a 
great  abundance  in  the  vegetation.  From  the  high  lati- 
tude to  which  warm  weather  extended  in  that  period, 
Agassiz  remarks  that  the  Tertiary  age  may  be  called  the 
geological  summer. 

374.  Strata  of  Diatoms.  —  There  are  found  here  and 
there  in  the  Tertiary  system  strata  which  are  made  up 
of  what"  were  formerly  supposed  to  be  infusorial  animals. 
The  diatoms,  however,  which  compose  by  far  the  largest 
proportion  of  the  rock,  are  now  ascertained  to  be  vege- 
table, and  not  animal.     I  have   already  noticed  these 
plants,  and  the  strata  which  they  have  formed,  in  §  240, 
and  will  not  dwell  on  them  here.     As  these  diatomaceae 
are  so  exceedingly  minute,  a  very  long  age  must  have 
been  required  for  the  accumulation  of  thick  beds  of  silex 
from  their  remains,  such  as  are  found  about  Richmond, 
in  this  country,  and  in  Bilin,  in  Bohemia.     As  it  takes 
187  millions  of  them  to  make  a  single  grain,  it  could  have 
been  only  by  the  contributions  of  countless  generations 
of  them  that  a  stratum  of  from  14  to  30  feet  in  thickness 
was  laid  down. 

375.  Tertiary  Animals. — So  far  to  the  north  was  the 
climate  warm  in  the  Tertiary  age,  that  as  it  was  with 
plants,  as  stated  in  §  373,  so  it  was  with  animals — such 
kinds  of  animals  as  now  flourish  in  tropical  climates  were 
then  in  high  northern  latitudes,  crocodiles,  turtles,  gigan- 
tic sharks,  pachydermatous  quadrupeds,  etc.     The  earli- 
est remains  of  birds  are  found  in  the  strata  of  the  Eo- 
cene period,  the  dawn  of  the  Tertiary.     So  also  serpents 


AGE    OF    MAMMALS. 


267 


first  appear  in  the  Tertiary  strata.  Not  a  species  offish, 
or  reptile,  or  bird,  or  mammal  of  the  Tertiary  period 
is  in  existence  at  the  present  time.  These  classes  of  an- 
imals are  in  contrast  with  mollusks  in  this  respect,  for 
many  of  the  latter,  as  you  saw  in  §  368,  coming  into  ex- 
istence in  the  Miocene  and  Pliocene  periods  of  the  Ter- 
tiary, are  living  still  in  the  midst  of  the  mollusks  of  the 
present  period  that  were  created  long  ages  after  them. 

376.  Fishes. — The  remains  of  fishes  abound  in  the  ter- 
tiary strata.  The  most  intef  esting  are  the  Shark  family, 
which  flourished  in  great  numbers  both  in  Europe  and 
America.  Some  of  them  were  monstrous  in  size.  In 
Fig.  160  is  represented  the  tooth  of  the  Carcharodon 


268  GEOLOGY. 

megalodon,  the  largest  species  of  shark,  which  must  have 
been  100  feet  in  length.  The  sharks  of  the  present  time 
are  large,  and  are  justly  very  much  feared,  but  they  are 
"  mere  pigmies,"  says  Hitchcock,  "  compared  with  those 
that  swam  in  the  seas  which  washed  the  shores  of  North 
and  South  Carolina  in  the  Eocene  and  Miocene  periods." 
These  terrific  monsters,  besides  being  much  larger  than 
the  sharks  of  the  present  age,  were  much  more  numerous 
than  now. 

377.  Reptiles. — Some  eighteen  or  twenty  species  of 
crocodiles  flourished  in  the  Tertiary  period,  while  there 
are  only  seven  or  eight  at  the  present  time.     The  croco- 
diles whose  remains  are  found  in  the  London  clay  were 
like  those  which  are  now  living  in  the  island  of  Borneo. 
There  were  about  seventy  species  of  turtles  and  tortois- 
es in  the  Tertiary  period.     Dana  speaks  of  the  remains 
of  one  which  was  20  feet  in  length,  and  whose  feet  must 
have  been  as  large  as  those  of  a  rhinoceros. 

378.  Mollusks. — Up  to  the  Tertiary  period  the  mol- 
lusks  were  all  of  species  that  do  not  exist  at  the  present 
time,  but  in  this  period  the  geologist  reckons  the  chro- 
nology of  the  strata  by  the  relative  percentage  of  extinct 
and  existing  shells  in  them.     To  do  this  the  general  clas- 
sification of  Lyell  (§  368)  is  adopted,  and  subdivisions, 
more  or  less  numerous,  are  made  under  it.    In  some  cases 
a  stratum  of  rock  is  composed  almost  wholly  of  shells, 
perhaps  almost  entirely  of  one  kind.     Sometimes  there 

is  much  variety  in  adja- 
cent  strata.  As  an  illus- 
tration,  I  will  give  you 
the  arrangement  of  a  clift' 
on  the  bank  of  the  James 
River,  Va.,  represented 
in  Fig.  161.  We  have 
here,  1.  Six  feet  of  sand 
and  clay.  2.  One  foot  of 
reddish  clav.  3.  A  band 


AGE    OP   MAMMALS.  269 

'of  small  pebbles  a  few  inches  thick.  4.  A  layer  of  sand 
three  feet  thick,  containing  shells  called  Chama  and  Ve- 
nus difformis.  5.  A  stratum  four  feet  thick,  consisting 
mostly  of  a  compact  mass  of  Chama  and  Area  centena- 
ria.  6.  A  stratum  two  feet  thick,  mostly  of  large  Pec- 
tens.  7.  Another  stratum  of  Chama,  with  Area  centena- 
ria,  Panopea  reflexa,  about  six  feet  in  depth.  8.  A  sec- 
ond layer  of  Pectens,  with  Ostrea  compressirostra,  one 
foot  thick.  9.  Another  stratum  of  Chama  three  feet 
thick.  10.  A  stratum  of  Peetens  and  Ostrea  five  feet 
thick.  When  the  shells  are  very  perfect  we  know  that 
the  animals  that  inhabited  them  lived  and  died  on  the 
spot,  and  that  the  strata  were  formed  very  gradually  in 
still  water.  We  make  a  different  inference  when  the 
shells  are  much  broken  up.  On  the  York  River,  in  Vir- 
ginia, there  is  a  porous  rock,  in  some  places  forty  feet 
in  height,  which  is  made  up  almost  wholly  of  comminu- 
ted shells.  Here  was  no  still  water,  but  there  were  the 
rush  of  the  tide  and  the  breaking  of  the  surf  during  all 
the  time  that  this  rock  was  being  deposited. 

379.  Indusial  Limestones. — Another  example,  in  addi- 
tion to  those  already  mentioned,  of  the  contributions  of 
small  animals  in  the  work  of  rock-making  we  have  in  the 
indusial  limestones  in  the  ancient  province  of  Auvergne, 
in  the  central  part  of  France.  The  agent  in  this  case 
was  the  larva  of  a  species  of  fly,  allied  to  the  common 
caddis-worm  of  the  angler  of  the  present  day.  We  find 
now  that  the  larvae  or  grubs  of  different  species  use  va- 
rious materials  for  their  indusia,  or  covers,  some  gluing 
together  small  bits  of  wood,  others  choosing  grains  of 
sand,  and  others  still  the  shells  of 
small  mollusks.  One  of  the  last 
is  seen  in  Fig.  162.  The  animal 
is  in  a  tube  which  it  has  con- 
structed for  itself  of  minute  shells, 
and,  living  in  this,  it  thrusts  its 
head  and  a  portion  of  its  body 


270  GEOLOGY. 

out  in  search  of  its  food.*  "It  is  evident,"  says  Mr.' 
Eley,  an  English  geologist,  "  that  the  larger  of  the  an- 
cient lakes  of  Auvergne  was  inhabited  by  a  species  of 
this  family,  and  that  they  swarmed  in  it  in  a  remarkable 
manner ;  for  their  cases,  incrusted  with  a  calcareous  mat- 
ter, are  seen  to  form  there  thick  layers  of  limestone — 
called  indusial,  from  this  strange  origin — which  altern- 
ate with  the  more  usual  kinds  of  marl  through  a  thick- 
ness of  several  hundred  feet."  These  indusial  strata  are 
eight  or  ten  feet  thick,  and  extend  over  an  area  of  many 
square  miles.  When  you  are  told  that  one  of  the  cases 
or  tubes  contains  over  a  hundred  shells,  and  ten  or  twelve 
tubes  may  be  counted  in  a  single  cubic  inch  of  rock,  you 
may  have  some  idea  of  the  countless  myriads  of  minute 
mollusks  which  must  have  formerly  lived  and  died  in  ev- 
ery part  of  this  region,  and  of  the  length  of  time  required 
for  the  formation  of  the  strata  constructed  chiefly  from 
their  shells. 

380.  Mammals. — Animals  of  this  class  were  specially 
prominent  in  the  scenes  of  this  age.  Tapir-like  pachy- 
derms flourished  largely  in  the  early  part  of  the  age,  but 
as  we  come  to  its  latter  portions  in  the  examination  of 
the  strata,  we  find  the  mammals  more  like  those  of  the 
present  age.  Still,  there  is  not  a  single  species  of  all 
those  that  have  this  resemblance  which  is  not  now  ex- 
tinct. There  are  some  localities  that  are  peculiarly  rich 
in  remains  of  the  mammals  of  the  Tertiary.  In  the  Up- 
per Missouri  region,  in  this  country,  among  other  re- 
mains, there  have  been  found  those  of  three  species  of 
camel,  a  rhinoceros  as  large  as  the  Indian  species,  a  mas- 
todon, an  elephant,  a  wolf  larger  than  any  species  of  the 
present  day,  four  or  five  species  of  the  Horse  family,  etc. 
It  seems  strange  to  us  that  some  of  these  animals  should 
exist  in  such  a  locality,  so  far  from  the  haunts  of  similar 
animals  in  the  present  period  ;  but  more  strange  still  is 

*  For  a  full  description  of  the  habits  of  these  animals,  see  my  Nat- 
ural History,  §  459. 


AGE    OF    MAMMALS.  271 

it  to  think  of  monkeys  as  being  in  England,  and  yet  re- 
mains of  them  are  found  in  that  locality  as  far  back  even 
as  the  strata  of  the  Eocene. 

381.  Cetacea. — The  most  remarkable  of  the  Cetaceans 
of  this  age  is  the  Zeuglodon  cetoides,  a  tooth  of  which 
is  seen  represented  of  its  natural  size  in  Fig.  163.  The 


tooth  is  yoke-shaped,  and  hence  the  name  given  to  the 
animal,  which  is  derived  from  two  Greek  words,  zevglon, 
a  yoke,  and  odons,  tooth.  Its  remains  were  first  noticed 
by  Dr.  Harlan,  of  Philadelphia,  who  in  1832  described  a 
vertebra  weighing  44  pounds,  which  was  brought  from 
the  Washita.  He  referred  the  animal  to  which  it  be- 
longed to  a  new  genus,  which  he  called  Basilosaurus — 
that  is,  king  of  the  Saurians,  supposing  it  to  be  reptilian 
in  character.  It  has  since,  however,  been  proved  to  be- 
long to  the  whale  tribe.  Its  vertebra  were  formerly  so 
abundant  in  the  State  of  Alabama  that  they  were  used 
very  commonly  in  making  walls.  Some  of  them  are  a 
foot  and  a  half  in  length,  and  a  foot  in  diameter.  Lyell 
saw  the  vertebral  column  of  one  skeleton  which  extend- 
ed on  the  ground  nearly  70  feet. 


GEOLOGY. 


382.  Pachydermata. — The  most  prominent  of  the  mam- 
mals of  the  early  Tertiary  were  the  pachydermatous 
quadrupeds.  Some  of  these  animals  are  represented  in 
Fig.  164.  The  one  on  the  right  is  the  Palaeotherium. 


Fig,  164. 

This  is  intermediate  in  shape  and  character  between  the 
tapir  and  rhinoceros  of  the  present  day.  There  are  about 
twelve  species,  varying  much  in  size,  the  largest  being 
of  the  size  of  a  rhinoceros,  the  smallest  about  as  large  as 
a  sheep.  The  other  two  animals,  the  Anoplotherium  in 
the  middle,  and  the  Ziphodon  on  the  left,  were  lighter  in 
their  construction,  though  having  the  same  general  char- 
acter with  the  Pala30therium.  These  are  representatives 
of  a  large  class  of  mammals  that  flourished  in  that  age 
in  the  forests,  on  the  plains,  and  by  the  lake  and  river- 
swamps.  They  were  curious  creatures,  uniting  in  them- 
selves the  peculiarities  of  two  or  more  animals  of  differ- 
ent, even  often  of  opposite  character,  such  as  tapir,  sea- 
cow,  hog,  rhinoceros,  ass,  camel,  and  antelope. 

383.  Cuvier's  Investigations. — The  remains  of  these 
pachydermata  have  been  found  in  great  abundance  in 
the  strata  of  what  is  called  the  Paris  basin.  Four  fifths 
of  the  fifty  species  of  quadrupeds  whose  remains  are 
found  there  belong  to  this  tribe,  which  is  represented  in 
the  present  age  by  only  four  species,  so  different  are  the 
prevalent  forms  of  animal  life  now  from  what  they  were 


AGE    OF   MAMMALS.  273 

in  the  Eocene  of  the  Tertiary.  Guvier  was  the  first  to 
develop  the  true  character  of  the  remains  in  the  Paris 
basin.  Soon  after  he  had  investigated  the  fossil  ele- 
phants (to  be  noticed  hereafter),  some  bones  found  in 
the  quarries  of  Montmartre,  near  Paris,  were  brought  to 
him  for  examination.  He  at  once  instituted  comparisons 
between  these  and  the  bones  of  various  animals  of  the 
present  age,  in  order  to  ascertain  the  character  of  the 
animals  to  which  the  fossil  bones  belonged.  He  soon 
decided  that  they  were  pachyderms ;  and  at  length,  with 
his  knowledge  of  the  relations  of  bones  to  each  other  and 
to  other  parts  of  the  frame,  he  was  able,  from  a  few  bones, 
such  as  those  of  the  head,  the  jaws,  some  teeth,  and  a  few 
of  the  vertebra?,  to  fill  out  the  deficiencies,  and  he  drew 
the  outlines  of  two  animals  as  he  supposed  them  to  have 
been,  the  Pala30therium  and  Anoplotherium,  represented 
in  Fig.  164.  He  presented  the  subject  to  the  French 
Academy,  averring  that  the  fossil  bones  belonged  to  ani- 
mals of  a  creation  previous  to  the  present  animal  crea- 
tion, and  he  therefore  called  the  larger  animal  Pala3othe- 
rium,  from  two  Greek  words, palaios,  ancient,  and  theri- 
on,  animal.  These  views  were  received  variously  by  sci- 
entific men,  some  disbelieving,  many  doubting,  and  those 
only  believing  who  had  paid  some  attention  to  compara- 
tive anatomy.  As  the  investigation  proceeded,  complete 
skeletons  of  the  animals  were  after  a  while  found  in  the 
strata,  and  the  outlines  made  by  Cuvier  were  shown  to 
be  correct,  and  his  views  were  universally  adopted. 

384.  Dinotherium. — Farther  along  in  the  Tertiary  than 
the  pachyderms  of  the  Paris  basin  appeared  a  monstrous 
pachyderm  of  a  singular  composite  character,  called  the 
Dinotherium,  represented  in  Fig.  165  (p.  274).  Its  re- 
mains have  been  found  in  various  parts  of  Europe,  the 
most  perfect  being  a  fine  skull  found  in  Germany.  The 
figure  gives  the  animal  as  it  was  restored  by  Professor 
Kaup  from  the  scanty  remains  which  have  been  obtain- 
ed. As  none  of  the  bones  of  the  limbs  have  as  yet 
M2 


274 


GEOLOGY. 


Fig.  165. 

been  found,  there  is  some  difference  of  opinion  among 
naturalists  as  to  the  true  character  of  the  animal,  some 
supposing  it  -to  be  much  like  an  elephant,  and  others  al- 
lying it  to  the  dugong,  a  swimming  pachyderm,  for  the 
description  of  which  I  refer  you  to  my  Natural  History, 
§  195.  There  is,  in  truth,  in  this  strange  animal,  a  mix- 
ture of  the  peculiarities  of  the  elephant,  hippopotamus, 
tapir,  and  dugong.  If  it  be  a  quadruped,  it  is  the  largest 
of  all  the  quadrupeds  that  ha^e  lived  on  the  globe,  being 
larger  than  even  the  mammoth  and  mastodon,  hereafter 
to  be  noticed.  It  was  probably  eighteen  feet  long.  Its 
skull  is  nearly  four  feet  in  length,  its  upper  jaw  being 
shaped  like  that  of  the  elephant,  for  the  attachment  of  a 
trunk.  It  had  two  enormous  tusks  on  the  lower  jaw, 
curving  downward  like  those  of  the  walrus.  It  proba- 
bly lived  chiefly  in  the  water,  like  the  hippopotamus.  Its 
diet,  as  we  know  by  its  teeth,  was  vegetable,  and  it  un- 
doubtedly used  its  tusks  to  tear  up  the  roots  of  aquatic 
plants  by  a  rake-like  action  from  the  beds  of  rivers  and 
lakes.  Perhaps,  too,  it  used  its  tusks  as  hooks  for  draw- 
ing its  huge  unwieldy  body  up  banks,  and  even  along 
upon  the  ground  if  it  had  no  real  legs. 

385.  Tertiary  Mountain-making. — There  was,  as  you 
have  already  seen,  considerable  mountain-making  during 
the  Tertiary  period,  and  therefore  much  change  of  eleva- 
tion and  flexure  of  the  strata,  with  more  or  less  of  frac- 


AGE    OF    MAMMALS.  275 

tures.  The  Rocky  Mountains,  which  began  to  be  raised 
at  the  close  of  the  Cretaceous  age,  did  not  reach  then- 
full  height  till  late  in  the  Tertiary  period.  The  Pyrenees 
and  Carpathians  were  lifted  up  in  the  Eocene  part  of  the 
Tertiary.  It  was  during  the  Tertiary  age  that  the  Alps, 
Appenines,  the  Caucasian  range,  and  the  Himalayas  at- 
tained, very  nearly  at  least,  to  their  present  altitude.  On 
the  completion  of  this  period  the  mountains  of  the  earth 
were  very  generally  raised  to  their  full  height. 

Observe  that  these  mountains,  which  were  raised  thus 
late,  comparatively,  in  the  course  of  the  formation  of  the 
continents,  are  many  of  them  of  very  great  height.  Com- 
pare them  with  the  Alleghanies,  that  were  raised,  as  is 
supposed,  at  the  close  of  the  Carboniferous  age.  The 
contrast  is  still  greater  if  you  compare  them  with  the 
Laurentian  Hills,  so  called,  in  Canada,  which  were  the 
mountains  in  the  Azoic  age  on  that  long  island,  the  germ 
of  the  North  American  continent,  spoken  of  in  §  267. 
These  first  mountains  of  the  earth  are  nowhere  more 
than  1500  or  2000  feet  above  the  level  of  the  sea.  The 
reason  of  this  difference  between  the  older  and  more  re- 
cently formed  mountains  is  thus  given  by  Agassiz  in 
speaking  of  the  Laurentian  Hills.  "  Their  low  stature, 
as  compared  with  that  of  more  lofty  mountain  ranges,  is 
in  accordance  with  an  invariable  rule,  by  which  the  rela- 
tive age  of  mountains  may  be  estimated.  The  oldest 
mountains  are  the  lowest,  while  the  younger  and  more 
recent  ones  tower  above  their  elders,  and  are  usually 
more  torn  and  dislocated  also.  This  is  easily  understood 
when  we  remember  that  all  mountains  and  mountain 
chains  are  the  result  of  upheavals,  afll  that  the  violence 
of  the  outbreak  must  have  been  in  proportion  to  the 
strength  of  the  resistance.  When  the  crust  of  the  earth 
was  so  thin  that  the  heated  masses  within  easily  broke 
through  it,  they  were  not  thrown  to  so  great  a  height, 
and  formed  comparatively  low  elevations,  such  as  the 
Canadian  hills,  or  the  mountains  of  Bretagne  and 


276  GEOLOGY. 

But  in  later  times,  when  young,  vigorous  giants,  such  as 
the  Alps,  the  Himalayas,  or,  later  still,  the  Rocky  Mount- 
ains, forced  their  way  out  from  their  fiery  prison-house, 
the  crust  of  the  earth  was  much  thicker,  and  fearful  in- 
deed must  have  been  the  convulsions  which  attended 
their  exit." 

With  the  raising  of  so  many  mountains,  the  great  sys- 
tems of  rivers  alluded  to  in  §  165  were  begun;  but,  as 
they  were  not  completed  till  the  next  age,  I  will  defer 
the  consideration  of  this  subject  till  I  come  to  speak  of 
that  age. 

386.  Tertiary  Volcanoes.  —  There  are  evidences  that 
volcanic  agencies  were  at  work  during  the  Tertiary  age 
in  various  parts  of  the  earth.  Such  evidences  have  been 
found  in  the  West  India  islands,  in  Central  America,  in 
parts  of  the  Andes,  and  on  the  eastern  continent  in 
France,  Italy,  Spain,  Greece,  and  the  island  of  Sicily. 
The  most  interesting  and  striking  evidences  are  found  in 
the  ancient  provinces  of  Auvergne,  Velais,  and  Vivarais, 
in  the  centre  of  France.  Many  hundreds  of  cones  are 
seen  there,  and  the  streams  of  lava  which  issued  from 
them  can  be  traced,  in  many  cases,  as  distinctly  as  those 
which  in  this  present  age  so  recently  have  flowed  from 
Vesuvius  or  Etna.  Some  of  these  cones  are  represented 
in  Fig.  166.  Many  of  them  have  been  preserved  with 


remarkable  distinctness.  This  is  owing  to  their  loose, 
porous  structure,  which  at  first  thought  would  be  con- 
sidered as  rendering  them  very  destructible.  The  ex- 
planation is,  that  all  the  rain  which  falls  is  absorbed  at 


AGE    OF   MAMMALS. 


277 


once  by  the  porous  mass,  so  that  there  are  no  rills  run- 
ning down  the  sides  of  the  cones  to  wear  them  away. 
The  highest  of  the  volcanoes  is  Mont  Dor,  in  Auvergne, 
which  was  several  thousand  feet  above  the  surrounding 
platform,  and  retains  now  the  shape  of  a  flattened  cone, 
broken  on  its  summit  into  several  rocky  peaks,  probably 
from  occasional  earthquakes  in  ages  long  gone  by,  and 
the  continued  influence  of  rain  through  not  merely  many 
centuries,  but  many  ages. 

387.  Basins. — From  the  disturbances  which  occurred 
in  the  Tertiary  period,  there  are  strata  found  in  some  lo- 
calities so  arranged  in  flexures  as  to  form  what  are  called 
basins.  Among  the  most  noted  of  these  are  the  basins 
of  London  and  Paris.  In  Fig.  167  is  represented,  in  a 


Fig.  167. 

rude  way,  that  of  London.  At  4  we  have  the  chalk  ly- 
ing upon  green  sand,  5.  Upon  the  chalk  lies  the  plastic 
clay,  so  called  because  in  France,  where  it  is  less  mixed 
with  other  materials,  it  is  extensively  used  in  pottery. 
Here  there  are  in  it  beds  of  flint  and  pebbles  alternating 
with  sands  and  clay.  Upon  it  lies  the  London  clay,  2, 
upon  which  the  city  of  London  stands.  It  varies  from 
two  to  six  hundred  feet  in  thickness,  is  of  a  dark  color, 
tough  in  texture,  and  having  mixed  with  it  here  and 
there  earth  of  a  green  color,  white  sand,  and  masses  of 
clayey  limestone.  At  6  is  the  River  Thames.  At  1,  1 
are  caps  of  marine  sand,  which  are  found  on  many  of  the 
hills  in  the  valley  of  the  Thames.  This  sand  probably, 
when  first  deposited,  formed  a  continuous  bed  over  the 
region,  but  has  been  excavated  with  a  part  of  the  Lon- 
don clay,  an  example  of  the  denuding  agency  of  water. 


278  GEOLOGY. 

With  such  a  basin  arrangement  of  strata  as  we  have 
here  and  at  Paris,  you  can  see  how  artesian  wells  can  be 
successful  in  both  of  these  localities,  as  noticed  in  Part 
I.,  §  120,  to  which  I  refer  you  for  the  explanation  of  their 
operation. 

388.  Tertiary  Continent-making. — In  the  Tertiary  age 
a  great  work  was  done  in  the  building  up  of  the  conti- 
nents. But  it  was  not  so  much  by  the  laying  down  of 
deposits,  though  these  were  vast  in  thickness  and  over 
extensive  areas,  as  it  was  by  elevating  strata  already 
made,  and  crumpling  them  up  in  various  quarters  into 
mountains.  The  work  of  this  period  is  thus  summed  up 
by  Dana.  "  There  was,  1,  the  finishing  of  the  rocky  sub- 
stratum of  the  continents ;  2,  the  expansion  of  the  conti- 
nental areas  to  their  full  limits,  or  their  permanent  recov- 
ery from  the  waters  of  the  ocean ;  3,  the  elevation  of 
many  of  the  great  mountains  of  the  globe,  or  consid- 
erable portions  of  them,  through  a  large  part  of  their 
height."  He  says,  also,  that  "  the  mass  of  the  earth 
above  the  ocean's  level  was  increased  two  or  three  fold 
between  the  beginning  and  end  of  the  Tertiary  period." 
In  this  country  there  was  a  mere  fringe  added*  along  its 
eastern  and  southern  edge,  but  in  the  west,  beyond  the 
Mississippi,  there  was  an  addition  of  vast  extent.  Tho 
North  American  continent,  with  its  triangular  shape,  had 
now  its  great  triangular  skeleton  of  mountain  ranges, 
as  Agassiz  calls  it,  completed,  shutting  in  that  immense 
area,  the  Mississippi  Valley.  The  Laurentian  Hills  on  the 
north,  making  the  base  of  the  triangle,  came  into  being 
in  that  first  long,  dark  age  of  the  world,  the  Azoic  age ; 
the  range  of  Alleghanies,  making  the  eastern  limb,  were 
raised  probably  at  the  close  of  the  Carboniferous  period; 
and  the  Rocky  Mountains,  the  western  limb,  were  thrust 
up  in  the  Tertiary  age.  The  continent  was  now  essen- 
tially completed,  the  only  great  works  yet  to  be  done 
being  the  filling  up  of  a  narrow  gulf  which  extended  to 
where  the  city  of  St.  Louis  now  is,  from  the  material 


AGE    OF   MAMMALS.  279 

brought  down  from  wide  regions  by  the  Mississippi  and 
Missouri  rivers,  and  the  building  up  of  the  peninsula  of 
Florida  by  the  coral  animals,  which  are  at  the  present 
time  building  as  busily  as  ever. 

389.  Post-tertiary  Period. — This  period  extends  from 
the  conclusion  of  the  Tertiary  to  the  advent  of  man. 
The  building  of  all  the  continents  was  now,  as  I  have  just 
said  of  North  America,  essentially  completed — that  is, 
the  land  had  now  reached  its  present  bounds,  and  its 
grand  ranges  of  prominences  were  raised  to  their  des- 
tined heights.     But  there  needed  to  be  a  greater  diver- 
sification of  surface  than  had  as  yet  been  effected — a  di- 
versification for  the  most  part  in  detail.     Hills  and  val- 
leys were  to  be  made ;  stones  of  various  sizes  were  to-be 
scattered  over  the  surface ;  rivers  were  to  be  extended 
and  multiplied ;  and  terrace-like  formations  were  to  be 
made   along  rivers,  and  lakes,  and  seas.     Moreover,  it 
was  necessary  that  much  rock  should  be  broken  and 
ground  up,  to  make  a  sufficient  quantity  of  fertile  earth 
for  man  and  the  accompanying  races  of  animals.     All 
this  was  done  by  the  agency  of  water  in  its  two  forms, 
liquid  and  solid,  as  you  will  see  as  I  proceed. 

390.  Divisions.  —  This  period  has  been  variously  di- 
vided.    As  the  system  is  developed  in  this  country,  it 
is  divided  by  Dana  into  three  epochs.     First  is  the  Gla- 
cial, when,  in  the  higher  latitudes,  the  land  was  raised 
much  above  its  present  elevation,  and  arctic  cold  pre- 
vailed over  a  large  portion  of  the  earth  from  either  pole 
toward  the   equator,  producing  glaciers   and  icebergs. 
The  second  is  the  Champlain^  so  named  because  the 
beds  of  this  epoch  are  well  developed  at  Lake  Cham- 
plain.     In  this  epoch  there  wasr  in  strong  contrast  with 
the  Glacial,  a  depression  of  the  surface  below  its  present 
level,  and  there  were  deposits  of  three  kinds — river-bor- 
der, lacustrine,  and  marine,  or  sea-border.     As  the  land 
sank  down,  the  glaciers  and  icebergs  melted,  and  the  wa- 
ters swept  over  the  varied  surface  of  the  land,  producing 


280  GEOLOGY. 

great  changes  in  the  disposition  of  its  loose  materials. 
The  third  epoch  was  the  Terrace  period.  Now  there 
was  gradual  elevation  of  the  land  till  it  reached  its  pres- 
ent level,  the  waters  all  the  time  actirrg  upon  the  mate- 
rials laid  down  in  the  Champlain  epoch,  especially  in  the 
rivers.  This  action  made  terraces  skirting  rivers,  lakes, 
bays,  etc.,  which  fact  has  given  the  epoch  its  name.  It 
is  a  transition  epoch,  for  it  is  separated  by  no  well-de- 
fined line  from  the  succeeding  age,  the  age  of  Man. 

The  same  division  can  be  made  essentially  in  Europe. 
I  will  speak  of  each  epoch  separately. 

391.  Glacial  Epoch. — In  this  epoch,  the  summer  heat, 
which  prevailed  over  the  now  temperate  regions  during 
the  Tertiary  age,  was  s'ucceeded  by  arctic  cold.     The  cap 
of  ice  which  now  covers  each  pole  extended  then  far  to- 
ward the  equator.     In  this  country,  all  New  England, 
New  York,  and  other  parts  in  the  same  latitudes  were 
covered  by  it.     In  Europe,  those  parts  that  have  now 
glaciers  far  up  in  the  valleys  of  their  mountains  were 
then  covered  with  them  as  Greenland  is  now.     Ice  reign- 
ed then  all  over  Great  Britain.     The  change  in  tempera- 
ture was  a  gradual  one,  produced,  as  it  is  supposed,  by 
the  elevation  of  all  the  land  in  a  body  at  the  north  to 
a  much  higher  level  than  it  has  at  the  present  time. 
The  glaciers  of  that  period  moved  down  in  the  valleys 
as  the  glaciers  of  the  present  time  do.     One  moved  down 
the  valley  of  the  Connecticut,  another  down  the  valley 
of  the  Hudson,  etc.     They  produced  results  similar  to 
those  which  are  produced  by  glaciers  at  the  present  day, 
described  in  §  190.     Many  of  them  were  thicker  and  lar- 
ger than  present  glaciers,  and  produced,  therefore,  larger 
results.     There  were  then,  as  now,  icebergs  wherever 
the  glaciers  reached  to  water  instead  of  terminating  on 
land. 

392.  Drift. — As  a  consequence  of  the  action  of  glaciers 
and  icebergs  in  the  Glacial  period,  there  is  scattered  over 
all  the  northern  parts  of  America,  Europe,  and  Asia  wKif 


AGE    OF    MAMMALS.  281 

is  called  drift.  It  is  various  in  its  composition,  the  ma- 
terial being  sand  or  gravel,  or  boulders  of  various  sizes. 
Sometimes  the  boulders  are  mingled  with  the  sand  and 
gravel,  and  sometimes  they  are  separate.  When  the  ma- 
terials of  drift  are  in  manifest  layers,  and  to  some  extent 
sorted,  the  finer  and  coarser  alternating,  and  the  frag- 
ments are  rounded  and  smoothed,  it  is  called  modified 
drift.  Water  has  in  this  case  acted  upon  the  materials, 
and  laid  them  in  beds.  Now  of  all  this  material  which 
we  call  drift,  none  was  produced  where  it  lies,  but  it 
was  transported  to  its  localities,  and  for  the  most  part 
from  the  north  toward  the  south.  There  are  two  theo- 
ries in  regard  to  its  transportation — the  one  attributing 
the  result  to  glaciers,  and  the  other  to  icebergs — called 
respectively  the  glacier  and  the  iceberg  theory.  But  the 
facts  show  conclusively  that  neither  could  alone  accom- 
plish all  the  work,  and  that  both  must  have  been  more  or 
less  in  operation.  The  drift  must  have  produced  great 
changes  on  the  surface,  filling  up  valleys  here  and  there, 
making  lakes  to  overflow,  and  altering  the  courses  of  riv- 
ers. A  marked  instance  we  have  of  the  latter  change 
in  the  case  of  the  Niagara  River.  There  is  decisive  evi- 
dence that  the  bed  which  it  flowed  in,  from  the  whirl- 
pool onward,  until  the  Glacial  epoch  was  then  filled  up 
with  drift,  and  the  water  opened  for  itself  a  new  gorge 
through  solid  rock,  through  which  it  has  run  to  the  pres- 
ent time.  The  drift  is  by  no  means  confined  to  the  val- 
leys and  plains,  but  extends  high  up  on  the  sides  of 
mountains,  and  is  found  even  on  the  tops  of  some  of 
them,  as  Mount  Holyoke  and  Mount  Tom,  in  Massachu- 
setts. It  is  at  the  height  of  2000  feet  in  the  Green 
Mountains,  3000  on  Monadnock,  and  even  6000  on 
Mount  Washington. 

393.  Boulders.  —  These  are  angular,  or  more  or  less 
rounded,  according  to  the  amount  of  friction  to  which 
they  have  been  subjected  by  water  and  other  stones. 
They  vary  much  in  size,  and  while  they  commonly  do 


282  GEOLOGY. 

not  exceed  a  cubic  foot,  they  sometimes  reach  thousands 
of  cubic  feet  in  size,  and  thousands  of  tons  in  weight. 
The  boulder  on  which  the  colossal  statue  of  Peter  the 
Great  stands  in  St.  Petersburg  is  a  mass  of  granite 
weighing  1500  tons.  A  boulder  at  Whittingham,  Vt.,  a 
town  in  the  Green  Mountains,  is  43  feet  long  and  32  in 
average  width,  contains  40,000  cubic  feet,  and  weighs 
3400  tons.  The  distances  to  which  boulders  have  been 
transported  have  been  much  investigated.  The  ordinary 
distances  are  from  20  to  40  miles,  but  they  have  often 
been  carried  60,  or  even  100  miles.  Hitchcock  speaks 
of  some  boulders  found  in  Ohio  and  Michigan  which 
came  from  the  ancient  azoic  rocks  of  Canada,  and  calcu- 
lates that  they  must  have  been  brought  from  a  distance 
of  from  400  to  600  miles.  These  distances  are  discov- 
ered by  comparing  the  boulders  with  the  rocks  of  the 
country,  thus  tracing  them  back  to  the  sources  from 
which  they  came.  Sometimes  great  boulders  have  been 
carried  across  deep  valleys.  Thus  the  monstrous  one  in 
Whittingham  was  transported  across  a  valley  1000  feet 
deep,  and  another  on  the  Hoosac  Mountain,  in  Massa- 
chusetts, came  across  a  valley  1300  feet  deep. 

Sometimes  many  square  miles  are  almost  covered  with 
boulders  of  various  sizes.  This  is  often  seen  in  the  hilly 
parts  of  New  England.  A  singular  circumstance  in  re- 
gard to  the  disposition  of  boulders,  first  pointed  out  by 
Hitchcock,  is  the  arrangement  of  them  in  long  trains. 
There  are  two  nearly  parallel  trains  in  Massachusetts, 
extending  from  between  Canaan  and  Lebanon,  one  of 
them  to  a  distance  of  20  miles  and  the  other  10.  They 
are  from  300  to  400  feet  in  width,  and  are  about  half  a 
mile  apart.  It  is  a  singular  fact  that  they  cross  two 
ranges  of  mountains  which  are  100  feet  higher  than  the 
source  from  which  the  stones  came.  The  boulders  are 
most  of  them  large,  one  of  them  weighing  over  2000 
tons,  and  their  angles  are  but  little  rounded,  showing 
that  they  have  been  subjected  to  but  little  friction.  Did 


AGE    OF    MAMMALS.  283 

two  enormous  icebergs  float  side  by  side  slowly  over 
that  region,  dropping  their  freight  of  stones  as  they 
melted  away?  This  is  the  only  supposition  we  can 
make,  but  this  is  not  at  all  satisfactory. 

394.  Glacial  Markings. — In  speaking  of  the  effects  of 
glaciers  in  §  190,  I  referred  to  various  markings  made 
by  them  on  the  rocks  of  ftieir  beds.  Similar  markings 
are  found  on  the  sides  of  mountains,  and  on  the  faces  of 
rocks  where  the  glaciers  and  icebergs  of  the  Post-ter- 
tiary age  moved  along.  We  find  them  every  where  in 
the  tracks  of  boulders.  There  is  great  variety  in  them. 
Sometimes  there  are  deep  furrows,  and  sometimes  mere 
scratches.  Sometimes  there  are  lines  as  delicate  as  if 
made  by  the  tool  of  an  engraver,  and  sometimes  the  sur- 
face of  a  stone  susceptible  of  polish  is  as  smooth  as  it 
would  be  if  it  were  artificially  polished  in  the  shop  of 
a  manufacturer.  Sometimes  rocky  ridges  have  been 
rounded  and  smoothed,  giving  them  an  undulating  ap- 
pearance, like  the  roches  montonnees,  or  embossed  rocks 
seen  in  the  Alps,  the  result  of  the  action  of  glaciers  of 
the  present  time,  as  represented  in  Fig.  42.  It  is  evi- 
dent that  most  of  these  markings  must  have  been  made 
by  glaciers,  and  not  by  icebergs.  While  icebergs  can 
plow  up  dirt,  and  sand,  and  gravel,  and  crush  rocks,  it 
requires  the  firm,  slow,  steady  movement  of  the  glacier, 
holding  its  rocky  tools  imbedded  in  the  ice,  to  make  the 
regular  parallel  grooves  and  lines,  and  the  polished  sur- 
faces. And,  in  proof  of  the  correctness  of  this  view,  we 
find  a  striking  resemblance  between  the  efiects  of  mod- 
ern glaciers  on  the  rocks  and  those  marks  which  appeal- 
where  the  glaciers  of  the  Post-tertiary  age  were  supposed 
to  be.  Still  there  is  some  coarse  and  irregular  work,  as 
we  may  term  it,  which  must  have  been  done  by  icebergs, 
as,  for  example,  the  making  of  furrows  and  valleys  on 
the  summits  of  some  of  the  lesser  mountains. 

The  glacial  markings  are  found  abundantly  on  high 
mountains  as  well  as  in  valleys  and  on  plains.  On  the 


-284  GEOLOGY. 

Green  Mountains  they  are  found  at  the  height  of  GOOD 
feet. 

395.  Champlain  Epoch. — As  the  land  elevated  in  the 
Glacial  epoch  subsided,  and  water  rose  over  it,  the 
Champlain  epoch  was  ushered  in.  It  found  a  vast  quan- 
tity of  material  which  had  been  broken  up  by  the  ice  of 
glaciers  and  icebergs,  and  transported  by  them  from  the 
sources  from  which  it  was  obtained,  mostly  in  southern 
directions,  and  to  greater  or  less  distances.  The -finer 
portions  of  this,  the  gravel,  and  sand,  and  mud,  the  mov- 
ing waters  of  this  epoch  carried  about  and  laid  down  in 
widely-extended  strata.  These  formations  are  alluvial, 
the  term  being  derived  from  the  Latin  word  alluo^  to 
wash.  Boulders  never  are  found  lying  upon  these  beds, 
for  they  were  scattered  by  the  glaciers  and  icebergs  be- 
fore these  strata  were  laid  down.  They  are  often  envel- 
oped and  covered  up  by  the  strata.  They  are  often  also 
found  on  elevations  in  the  neighborhood  of  Champlain 
strata.  In  such  cases  there  may  have  been  once  some  of 
the  finer  material  of  the  drift  mingled  with  them,  and  this 
may  have  been  washed  away,  the  water  not  being  able  to 
remove  the  boulders  themselves.  As  the  land  subsided  or 
sunk  down  extensively  in  this  epoch,  some  of  the  deposits 
occurred  on  very  high  elevations.  Hitchcock  mentions 
beaches  of  these  deposits  at  great  heights  in  the  Green 
and  the  White  Mountains,  one  at  the  Franconia  Notch 
being  2665  feet  above  the  level  of  the  sea.  The  subsi- 
dence of  the  land  at  the  north  during  this  epoch,  lessen- 
ing the  amount  of  it  above  the  surface  of  the  water,  and 
so  removing  the  arctic  cold,  which  the  raising  of  the  land 
in  the  Glacial  period  had  produced  (§  391),  melted,  of 
course,  the  glaciers  of  the  temperate  regions.  This  cre- 
ated at  the  outset  of  this  epoch  a  great  flow  of  waters 
over  the  continents,  which  carried  with  them  large  quan- 
tities of  the  smaller  materials  of  the  drift.  The  deposi- 
tion of  these  was  much  modified  by  the  lakes  and  rivers 
which  already  existed,  and,  in  return,  also  made  many 


AGE    OF    MAMMA 

changes  in  them.  It  is  difficult,  in  many 
guish  the  deposits  of  this  period  from  those  of  the  suc- 
ceeding one,  but  it  may  be  remarked  in  the  general  that 
the  river-plains  and  sea-beaches  of  the  Champlain  epoch 
are  at  the  present  day  elevated  plains  and  beaches — that 
is,  existing  at  higher  levels  than  the  terraces  made  in  the 
succeeding  period. 

396.  Terrace  Epoch.  —  As  you  have  seen,  there  have 
been,  in  the  course  of  the  formation  of  the  continents, 
many  extensive  subsidences  of  land,  letting  the  water 
prevail  for  a  time  where  it  had  been  dry  land  before. 
The  last  of  these  general  submergences  occurred  in  the 
Champlain  epoch.  In  the  next  epoch,  the  Terrace  pe- 
riod, the  movement  of  the  land  was  upward — a  move- 
ment of  emergence — which  went  on  until  the  land  ac- 
quired a  comparatively  settled  condition — that  is,  one 
from  which  it  has  not  varied,  to  any  great  degree,  since 
the  advent  of  man.  During  this  upward  movement  of 
the  Terrace  epoch  there  was,  to  a  considerable  extent,  a 
rearrangement  of  the  strata  laid  down  in  the  Champlain 
epoch.  In  this  rearrangement  the  formation  of  terraces 
was  so  common  that  this  has  given  the  name  to  the  pe- 
riod. The  term  terrace  is  applied  to  banks  of  loose  ma- 
terials skirting  the  sides  of  valleys  about  rivers  and 
lakes,  having  a  level  surface  on  the  top,  and  fronting  on 
the  river  or  lake  with  a  more  or  less  steep  escarpment. 
As  they  are  often  quite  numerous,  j*ising  above  each 
other  like  the  seats  of  an  amphitheatre,  but  differing 
much  in  width  and  in  the  lines  of  their  edges,  they  give 
great  variety  and  beauty  to  the  scenery,  especially  when 
the  habitations  of  men  are  built  upon  them,  which  is  oft- 
en done,  or  when,  as  is  sometimes  the  case,  they  are  used 
as  the  dwelling-places  of  the  dead.  Not  only  do  they 
vary  in  width  and  in  line  of  edge,  but  the  variety  is  oft- 
en increased  by  the  action  of  rain  with  the  currents 
caused  by  it  on  their  level-topped  surfaces.  You  see  in 
Figs.  168  and  169  (p.  286)  sections  of  two  series  of  ter- 


286 


GEOLOGY. 


Fig.  169. 

races.  In  Fig.  168,  at  the  right  hand,  is  represented  a 
section  of  the  bed  of  the  Connecticut  River,  lying  in  the 
alluvial  loam.  Here  there  are  seven  terraces  of  various 
widths,  the  upper  one  having  a  considerable  excavation 
in  it  from  the  continued  action  of  rain.  In  Fig.  169  is 
represented  a  set  of  terraces  at  another  locality  on  the 
Connecticut,  where  the  arrangement  is  somewhat  differ- 
ent. 

397.  How  Terraces  were  Formed. — Terraces  resulted 
from  the  action  of  water  on  the  modified  drift  as  the  land 
was  rising  from  its  subsided  condition  in  the  Champlain 
epoch.  In  other  words,  they  were  formed  by  the  natu- 
ral drainage  of  the  country  during  that  rise.  Of  course, 
various  circumstances  had  a  play  in  their  formation,  giv- 
ing them  variety  in  their  shape  and  arrangement.  The 


AGE    OF    MAMMALS.  287 

operation  of  the  chief  of  these  circumstances  is  stated  by 
Dana  after  this  manner.  Every  river  has  its  channel 
and  its  flood-plain,  the  latter  being  overflowed  whenever 
a  freshet  occurs,  as  stated  in  §  174.  Now  if,  when  the 
land  was  rising,  the  rise  was  chiefly  in  the  interior  of  a 
continent,  the  coast  being  little  changed,  the  rivers  run- 
ning toward  the  sea  would  have  their  slope  increased, 
and  so  greater  force  would  be  given  to  the  descending 
water.  The  result  of  this  would  be,  that  not  only  would 
the  channel  be  deepened,  but  a  part  of  the  flood-plain 
would  be  at  a  lower  level.  This  is  indicated  in  Fig.  170, 

A 


Fig.  170. 

where  a  is  the  bed  of  the  river,  and  b  the  flood-plain,  in 
the  Champlain  period.  The  change  thus  effected  by  the 
erosive  power  of  water  is  represented  by  the  dotted  line. 
This  would  leave  the  river  as  seen  in  Fig.  171,  with  b  for 


the  flood-plain,  and  a  terrace,  c.  As  soon  as  the  river  by 
this  process  attained  its  former  slope,  this  process  would 
stop.  Then,  if  the  same  rising  went  on,  another  similar 
result  would  occur.  And  so  with  a  succession  of  risings, 
or  perhaps  with  one  continued  rising,  several  terraces 
might  be  made,  as  represented  in  Figs.  168  and  169. 
There  are  many  circumstances  which  vary  the  results  of 
this  process,  and  make  the  terraces  irregular  in  height 
and  form.  There  are  also  other  processes  that  have  pro- 
duced terraces,  but  these  I  will  not  stop  to  describe. 

398.  Sea-beaches. — I  have  spoken  of  the  beaches  which 
were  made  in  the  Champlain  epoch.  When  these  are 
found  in  the  neighborhood  of  terraces  they  lie  at  a  high- 


288  GEOLOGY. 

er  level,  though,  as  they  were  formed  earlier  than  the 
terraces,  they  extend  down  under  them,  and  are  there- 
fore, geologically  speaking,  lower.  They  often  form  a 
sort  of  upper  terrace  in  the  series,  making  a  fringe  along 
the  sides  of  the  hills  that  shut  in  a  valley.  Though  ir- 
regular in  form,  they  have  a  certain  general  level,  if  ob- 
servation be  made  of  one  for  any  considerable  length 
along  the  hills  that  it  skirts.  They  consist  mostly  of 
sand  and  gravel,  all  the  stones  in  them  being  rounded, 
thus  showing  the  influence  of  long-continued  water  fric- 
tion. It  is  supposed  that  they  are  beaches  left  by  the  re- 
tiring sea,  as  the  submergence  of  the  Champlain  period 
passed  away. 

399.  Niagara  River.  —  Great  changes  occurred  in  this 
river  during  the  Post-tertiary  period.  Just  previous  to 
the  beginning  of  this  epoch  the  river  ran  in  entirely  a 
different  bed  from  what  it  now  runs  in  from  the  whirl- 
pool on  to  its  outlet  in  Lake  Ontario.  The  evidence  is 
this:  The  west  bank  of  the  gorge  at  the  whirlpool 
shows  the  beginning  of  a  deep  ravine  filled  with  drift  in 
the  form  of  gravel  and  sand,  and  this  ravine  can  be 
traced  on  to  Lake  Ontario.  The  inference  is  clear,  there- 
fore, that  the  water  ran  through  this  passage  of  four 
miles  to  the  lake  until  it  was  filled  up  with  drift  in  the 
Glacial  period ;  and  this  bed  being  filled  up,  the  wrater 
sought,  and,  to  a  great  extent  at  least,  made  for  itself, 
by  its  erosive  power,  another  passage,  the  one  in  which 
it  now  runs.  But  this  is  not  all.  The  water  has  effect- 
ed in  this  passage,  as  I  have  before  stated  in  §  183,  the 
removal  of  the  falls  from  the  neighborhood  of  Queens- 
town  back  seven  miles  to  their  present  position.  The 
process  by  which  this  has  been  done  has  been  explained 
in  §  183 ;  but  the  story  of  the  changes  which  have  been 
effected  in  the  Niagara  River  is  not  all  told  yet.  The 
still  waters  of  a  lake  once  lay  over  all  the  neighborhood 
where  the  falls  now  are,  for  there  are  lake  deposits  there, 
as  shown  by  the  fossils  which  the  strata  contain.  The 


AGE    OF    MAMMALS.  289 

tooth  and  other  bones  of  a  mastodon  found  in  these  de- 
posits show  that  they  were  laid  down  in  the  Champlain 
epoch,  for  this  animal  flourished  at  that  time. 

400.  Length  of  the  Post-tertiary  Age.— If  we  can  not 
make  some  approximation  to  an  estimate  of  the  length 
of  time  consumed  by  the  Post-tertiary  period,  by  calcu- 
lations from  the  rate  of  progress  in  the  recession  of  the 
Falls  of  Niagara,  we  can,  at  least,  see  that  the  age  was  a 
very  long  one.     The  recession  is  still  going  on,  and  va- 
rious observations  have  been  made  in  regard  to  it,  and 
estimates  have  been  based  on  those  observations.     The 
results,  as  worked  out  by  different  observers,  vary  great- 
ly.    Some  estimate  the  recession  as  high  as  three  feet  in 
a  year,  which  undoubtedly  is  far  beyond  the  fact.     Lyell 
estimates  it  as  averaging  one  foot  a  year.     This,  which 
Dana  says  is  certainly  large,  would  give  over  31,000 
years  for  the  whole  recession.     Mr.  Desor,  another  ob- 
server, inferred  from  the  data  which  he  ascertained  that 
it  was  "  more  nearly  three  feet  a  century  than  three  feet 
a  year."     Taking  it  at  three  feet  a  century,  the  whole 
would  require  over  a  million  of  years. 

401.  Post-tertiary  Rivers. — Rivers  are  a  part  of  the 
grand  apparatus  for  the  circulation  of  water  on  the  earth. 
Evaporation  carries  up  water  in  the  atmosphere  from 
over  the  whole  surface,  from  the  land  as  well  as  the  sea, 
and  the  vapor  thus  dissolved  in  the  air  is  condensed  into 
rain,  or  snow,  or  hail,  in  order  to  be  brought  back  to  the 
earth.    Falling,  it  gathers  in  little  streams,  which,  uniting 
together,  make  the  great  rivers  that  run  to  the  ocean. 
Now,  in  order  to  have  very  large  rivers,  two  things  are 
necessary — a  considerable  extent  of  land  to  afford  room 
for  the  union  of  many  streams  in  one,  and  the  presence 
of  great  mountains,  to  condense  the  vapor  rapidly  with 
their  tall,  cold  peaks.     Neither  of  these  conditions  was 
present  when  the  continents  began  to  form.     When  that 
long  island,  with  its  low   mountains,  the  germ  of  the 
North  American  continent,  was  lifted  up  in  the  Azoic 

N 


290  GEOLOGY. 

age  from  amid  the  waters,  no  such  rivers  as  the  Missis- 
sippi or  the  St.  Lawrence  were  upon  it.  And  the  grand 
river  systems  of  the  earth  were  not  fully  formed  till  after 
the  continents  were  expanded  to  their  full  limits,  and 
the  mountain  ranges  spoken  of  in  §  385  were  raised  up 
in  the  Tertiary  age.  The  Post-tertiary  age  then  was,  as 
stated  by  Professor  Dana,  "  the  era  of  the  first  grand 
display  of  completed  river  systems — of  the  first  Amazon, 
Mississippi,  Ganges,  Indus,  Nile,"  etc. 

402.  Terminal  Moraines  of  the  Ancient  Glaciers.— The 
glaciers  of  the  Post-tertiary  age  had  terminal  moraines, 
like  those  of  the  present  time  (§  190).  They  have,  of 
course,  been  much  altered  by  the  fluviatile  operations, 
that  is,  the  operations  of  moving  water,  which  produced 
such  great  effects  during  the  long  ages  of  the  Champlain 
and  Terrace  periods,  and  hence  it  is  that  I  notice  them 
here.  The  alterations  alluded  to  are  so  great  that  the 
resemblance  of  the  remains  of  these  ancient  moraines  to 
those  found  at*the  foot  of  the  glaciers  of  the  present  day 
is  not  obvious  to  the  common  observer.  It  is  only  the 
practiced  eye  of  the  skillful  geologist  that  can  discover 
it.  Agassiz,  Guyot,  and  others  have  investigated  this 
subject  by  extended  observations  in  some  of  the  locali- 
ties where  the  vast  glaciers  of  the  Glacial  period  lay,  es- 
pecially in  Switzerland  and  the  island  of  Great  Britain, 
and  have  traced  out  the  moraines  with  signal  success,  in 
spite  of  the  obliteration  of  their  distinctive  marks  by 
causes  which  have  been  acting  upon  them  for  ages. 
They  are,  for  the  most  part,  semicircular  in  shape,  the 
concavity  being  toward  the  direction  from  which  the  gla- 
cier moved  downward.  Sometimes  there  are  several 
of  these  semicircular  walls,  one  placed  within  another. 
Each  of  these  is  a  moraine,  the  outer  one  having  been 
formed  first,  and  the  others  one  after  another,  as  the  gla- 
cier retreated  or  became  shortened  (§  1 89).  In  the  pass- 
ing away  of  the  Glacial  age  there  was,  of  course,  a  con- 
stant diminution  of  the  extent  of  the  glaciers,  and  conse- 


AGE    OF   MAMMALS.  291 

quently  many  concentric  moraines  were  formed.  I  have 
spoken  of  the  moraines  as  walls,  but  many  of  them  are 
broad  and  extensive,  some  of  them  being  now  the  sites 
of  cities.  The  cities  of  Berne  and  Zurich  stand  on  mo- 
raines. Agassiz  mentions  a  moraine  through  which  a 
river  had  made  for  itself  a  passage,  and  a  village  occu- 
pies the  moraine  on  both  sides  of  the  river. 

These  ancient  moraines,  like  those  found  at  the  pres- 
ent time,  are  made  up  of  boulders,  pebbles,  gravel,  and 
sand,  indiscriminately  mixed  together.  But  their  com- 
position is  concealed  from  view  by  the  soil  which  has  ac- 
cumulated upon  their  surface  in  the  many  centuries,  even 
long  ages,  that  have  passed  since  their  formation,  and 
the  consequent  vegetation  that  has  sprung  up  upon  it. 
"  Time,"  says  Agassiz,  "  which  mellows  and  softens  all 
the  wrecks  of  the  past,  has  clothed  them  with  turf,  grass- 
ed them  over,  planted  them  with  trees,  sown  his  seed, 
and  gathered  in  his  harvests  upon  them,  until  at  last  they 
make  a  part  of  the  undulating  surface  of  the  country." 

403.  Soil  made  in  the  Post-tertiary  Period.  —  Soil  is 
merely  comminuted  rock.  Nothing  but  the  lowest  or- 
der of  vegetation  can  grow  on  solid  rock,  and  that  in  the 
scantiest  manner.  The  rock  must  be  broken  and  ground 
up  into  soil  in  order  to  be  the  basis  of  a  full  vegetation. 
The  various  agencies  by  irhich  this  is  done  have  been 
brought  to  your  view  in  various  parts  of  this  book.  They 
have  been  at  work  at  all  times  since  the  first  rocks  of  the 
Azoic  age  were  formed,  but  at  some  periods  more  than 
at  others.  They  were  especially  at  work  in  the  Post-ter- 
tiary period.  Quite  a  large  portion  of  the  soil  now  cul- 
tivated was  produced  then,  and  we  may  say  that  it  was 
one  of  the  great  objects  of  the  Creator,  in  the  operations 
of  that  period,  to  provide  soil  for  the  gardens  and  fields 
of  man,  who  was  to  come  upon  the  scene  of  action  in  the 
following  age.  The  rocks  were  broken  and  ground  up 
for  this  purpose  by  the  glaciers  and  icebergs  of  the  Gla- 
cial period,  and  the  work  of  grinding  and  sorting  was 


292  GEOLOGY. 

continued  on  through  the  Champlain  and  Terrace  peri- 
ods, the  water  making  piece  rub  against  piece,  great  and 
small,  thus  furnishing  the  small  particles  that  were  to  be 
the  nutritious  part  of  the  soil  which  it  was  to  spread 
over  the  country.  Hugh  Miller,  in  speaking  of  the  soil 
which  was  thus  furnished  to  Scotland,  holds  the  follow- 
ing language:  "It  is  but  a  tedious  process  through  which 
the  minute  lichen,  or  dwarfish  moss,  settling  on  a  surface 
of  naked  stone,  forms,  in  the  course  of  ages,  a  soil  for 
plants  of  greater  bulk  and  a  higher  order ;  and  had  Scot- 
land been  left  to  the  exclusive  operation  of  this  slow 
agent,  it  would  be  still  a  rocky  desert,  with  perhaps  here 
and  there  a  strip  of  alluvial  meadow  by  the  side  of  a 
stream,  and  here  and  there  an  insulated  patch  of  mossy 
soil  among  the  hollows  of  the  crags ;  but,  though  it  might 
possess  its  few  gardens  for  the  spade,  it  would  have  no 
fields  for  the  plow.  We  owe  our  arable  land  to  that  ge- 
ologic agent  which,  grinding  down,  as  in  a  mill,  the  up- 
per layers  of  the  surface  rocks  of  the  kingdom,  and  then 
spreading  over  the  eroded  strata  their  own  debris,  form- 
ed the  general  basis  in  which  the  first  vegetation  took 
root,  and  in  the  course  of  years  composed  the  vegetable 
mould.  '  A  foundering  land  under  a  severe  sky,  beaten 
by  tempests  and  lashed  by  tides,  with  glaciers  half  chok- 
ing up  its  cheerless 'valleys,  a»d  with  countless  icebergs 
brushing  its  coasts  and  grating  over  its  shallows,  would 
have  seemed  a  melancholy  and  hopeless  object  to  human 
eye  had  there  been  human  eyes  to  look  upon  it  at  the 
time ;  and  yet  such  seem  to  have  been  the  circumstances 
in  which  our  country  was  placed  by  Him  who,  to  "  per- 
form his  wonders," 

"Plants  his  footsteps  in  the  sea, 
And  rides  upon  the  storm," 

in  order  that,  at  the  appointed  period,  it  might,  accord- 
ing to  the  poet,  be  a  land 

"Made  blithe  by  plow  and  harrow." 
404.  Post-tertiary  Animals.  —  There  are  three  points 


AGE    OF   MAMMALS.  293 

worthy  of  remark  in  relation  to  the  animals  of  this  pe- 
riod. 1.  Their  great  size.  The  elephants,  bears,  lions, 
horses,  hyenas,  etc.,  were  much  larger  than  the  species 
of  these  animals  existing  at  the  present  time.  Perhaps 
the  difference  is  greater  in  the  sloths  than  in  any  other 
class  of  animals,  as  you  will  soon  see.  2.  The  division  as 
to  the  general  character  of  prevalent  species  in  the  dif- 
ferent continents  was  much  the  same  as  now.  Thus,  in 
the  eastern  continent,  the  Carnivorous  animals  predom- 
inated ;  in  North  America,  the  Herbivorous ;  in  South 
America,  the  Edentates;  and  in  Australia,  the  Marsu- 
pials, or  pouched  animals.  3.  Animals  that  were  in 
character  like  those  which  now  have  their  habitat  in 
warm  climates  lived  then  in  the  regions  that  are  now 
temperate,  and  in  some  cases  even  up  to  the  arctic  re- 
gions, as  in  the  case  of  the  elephant  and  rhinoceros  of 
Siberia.  Owen  says  of  England  at  this  period,  "Gigan- 
tic elephants  of  nearly  twice  the  bulk  of  the  largest  indi- 
viduals that  now  exist  in  Ceylon  and  Africa  roamed 
here  in  herds,  if  we  may  judge  from  the  abundance  of 
their  remains.  Two-horned  rhinoceroses  of  at  least  two 
species  forced  their  way  through  the  ancient  forests,  or 
wallowed  in  the  swamps.  The  lakes  and  rivers  were 
tenanted  with  hippopotamuses  as  bulky,  and  with  as  for- 
midable tusks  as  those  of  Africa."  Besides  these,  there 
were  tigers  larger  than  those  of  Bengal,  and  "  troops  of 
hyenas  larger  than  the  fierce  Hyena  crocuta  of  South 
Africa,  which  they  most  resembled,  crunched  the  bones 
of  carcasses  relinquished  by  the  nobler  beasts  of  prey, 
and  doubtless  themselves  often  waged  a  war  of  exterm- 
ination on  the  feebler  quadrupeds." 

I  will  now  go  on  to  notice  some  of  the  animals  that 
were  peculiar  to  this  period. 

405.  Post-tertiary  Elephants.  —  Elephas  primigenus, 
the  great  Siberian  mammoth,  was  a  third  taller  than  the 
largest  of  elephants  of  the  present  time,  and  was  twice 
as  heavy.  The  skeleton  of  this  animal  is  represented 


294  GEOLOGY. 

in  Fig.  172,  and  the   animal  itself  is   seen  in  Fig.  173, 


Fig.  173 


at  the  left  side.     You  observe  that  the  tusks  are  very 


AGE    OF    MAMMALS.  295 

much  longer  than  in  elephants  of  our  time,  and  that 
they  are  curved  upward  and  backward  with  a  broad 
sweep.  This  animal  had  long  black  hair,  mingled  with 
which  there  was  a  coat  of  reddish-brown  wool.  Such  a 
covering  undoubtedly  fitted  it  to  bear  a  colder  climate 
than  it  could  bear  with  the  ordinary  covering  of  ele- 
phants. At  the  same  time,  it  is  clear,  from  the  fact  that 
so  many  animals  of  the  same  kinds  with  those  that  now. 
flourish  in  warm  regions  then  existed  in  northern  lati- 
tudes, that  the  climate  of  the  far  north  was,  at  least, 
much  less  cold  than  it  is  now.  Indeed,  the  woolly  cov- 
ering of  the  mammoth  of  Siberia  simply  indicates  that 
the  climate  there  was  only  so  much  cooler  than  it  is 
where  elephants  are  accustomed  to  live  now,  that  this 
additional  covering  was  required  for  its  comfort,  and  yet 
it  was  not  so  cold  as  absolutely  to  forbid  the  existence 
of  animals  of  that  nature,  as  is  the  case  in  that  region  at 
the  present  time.  Besides,  if  arctic  cold  reigned  there 
as  it  does  now,  the  vegetation  could  not  have  been  suffi- 
cient for  the  sustenance  of  any  number  of  these  enor- 
mous quadrupeds.  The  remains  of  the  mammoth  show 
that  great  herds  lived  there.  The  tusks  which  are  found 
furnish  a  large  part  of  the  ivory  in  the  market.  The  Li- 
akhow  Islands,  lying  off  the  north  coast  of  Asia,  are  com- 
posed to  a  great  extent  of  mammoth  bones,  cemented 
together  by  sand  and  ice,  and  in  the  year  1821  as  much 
as  20,000  pounds  of  fossil  ivory  was  obtained  from  the 
island  of  New  Siberia,  some  of  the  tusks  weighing  near- 
ly 500  pounds.  The  mammoth  lived  in  herds  in  En- 
gland. Its  remains  have  also  been  found  in  North  Amer- 
ica, but  not  much  below  the  latitude  of  40°.  Below  this 
level  in  this  country  another  species  of  elephant  nour- 
ished, and  was  very  abundant  in  the  South,  in  the  Valley 
of  the  Mississippi.  On  the  island  of  Malta  there  have 
been  found  the  bones  of  a  pigmy  elephant  which  was 
about  the  size  of  a  calf. 

406.  The  St.  Petersburg  Skeleton. — There  is  a  skele- 


296  GEOLOGY. 

ton  of  a  mammoth  in  the  Imperial  Museum  at  St.  Peters- 
burg, the  story  of  which  is  interesting,  both  on  account 
of  the  circumstances  under  which  it  was  obtained,  and 
the  influence  which  it  had  upon  palaeontological  re- 
searches. The  story  is  this:  In  the  year  1799  a  Siberi- 
an fisherman  saw  a  rounded  mass  projecting  from  an  ice- 
bank  near  the  mouth  of  the  River  Lena.  The  summer 
weather  so  thawed  it  year  after  year  that  in  1803  the 
enveloping  ice  was  all  melted,  and  the  nucleus  of  this 
mound-like  projection  was  found  to  be  an  enormous  ele- 
phant. Though  it  had  been  there  not  merely  centuries, 
but  ages,  it  was  perfectly  preserved,  so  that  dogs  and 
wolves  fed  upon  it  as  upon  fresh  meat.  In  the  next 
year,  1804,  the  fisherman  cut  off  the  tusks,  which  weigh- 
ed 360  pounds,  and  sold  them.  In  1807  an  English  trav- 
eler, Mr.  Adams,  hearing  the  story,  visited  the  spot,  suc- 
ceeded in  collecting  all  the  bones  except  those  of  one 
foot,  which  were  supposed  to  have  been  carried  off  by 
wolves,  and  recovered  also  the  tusks.  He  also  found 
some  of  the  hair  and  wool,  and  parts  of  the  skin.  The 
name  Mammoth,  which  was  given  to  this  elephant,  is  a 
Siberian  word  meaning  earth-beast,  the  idea  of  the  na- 
tives being  that  the  mammoths  live  somewhere  under 
ground,  and  die  whenever  they  come  to  the  surface  and 
feel  the  influence  of  the  sun. 

407.  Cuvier's  Views. — The  discovery  of  the  Siberian 
elephant  was  the  occasion  of  many  speculations.  At 
first  it  was  thought  that  it  was  transported  to  this  high 
latitude  from  India  by  some  accident,  and  similar  re- 
mains found  shortly  after  in  Italy,  Germany,  etc.,  were 
supposed  to  belong  to  Carthaginian  elephants  brought 
into  Europe  by  the  armies  of  Hannibal ;  but  Cuvier  soon 
solved  the  mystery.  He  contended  that  an  Indian  ele- 
phant carried  to  Siberia  could  not  be  changed  in  the 
transportation, but  would  remain  an  Indian  elephant  still; 
and  as  the  bones  of  the  Siberian  mammoth  showed  that 
it  differed  essentially  in  some  respects  from  either  spe- 


AGE   OF   MAMMALS.  297 

cies  of  elephant  existing  at  the  present  time,  he  averred 
that  it  was  another  species.  He  averred,  farther,  that 
the  mammoth  was  a  species  belonging  to  a  previous  age 
and  now  extinct,  the  proofs  of  which  soon  became  very 
abundant  from  the  investigations  that  were  prompted  by 
the  teachings  of  Cuvier.  It  was  shortly  after  this  that 
the  discoveries  were  made  at  Montmartre,  as  noticed  in 
§  383,  and  these  awakened  a  general  interest  in  palaaon- 
tological  investigations. 

408.  Mastodons. — These  animals,  one  species  of  which 
is  represented  at  the  right  of  Fig.  173,  differed  so  decid- 
edly from  the  mammoths  as  to  constitute  another  genus. 
This  genus  is  now  extinct,  while  that  of  the  mammoths, 
or  elephants,  still  exists,  there  being  now  two  living  spe- 
cies, the  Indian  and  the  African  elephant,  for  descriptions 
of  which  I  refer  you  to  my  "  Natural  History,"  page  80. 
The  teeth  of  the  mastodon  differ  very  much  from  those 
of  the  mammoth,  having  the  enamel  raised  up  in  conical 
eminences,  as  seen  on  the  right  of  Fig.  174,  instead  of  the 


Fig.  1T4. 

arrangement  in  ridges  of  the  mammoth,  as  represented 
at  the  left  of  the  figure.  The  Mastodon  giganteus,  an 
entire  skeleton  of  which  is  in  the  Palaeontological  Gal- 
lery of  the  Britisji  Museum,  considerably  exceeded  in 
size  the  largest  elephant  of  the  present  time.  Its  bones 


298  GEOLOGY. 

are  found  only  on  the  North  American  continent,  and 
are  very  abundant  in  some  parts,  especially  in  a  saline 
morass  in  Kentucky  called  the  Big  Bone  Lick.  There 
is  a  tradition  prevailing  among  the  Indians  that  there 
existed  men  of  gigantic  stature  at  the  same  time  with 
the  colossal  animals  to  which  these  bones  belonged,  and 
that  both  were  destroyed  by  the  thunderbolts  of  the 
Great  Being ;  but  this,  like  many  other  traditions,  is  un- 
founded, for  no  bones  of  man  have  been  found  in  connec- 
tion with  those  of  the  mastodons.  There  have  been  five 
entire  skeletons  of  this  animal  dug  up  in  this  country. 
The  best  one  was  obtained  from  a  marsh  near  Newburg, 
New  York,  and  was  set  up  by  Dr.  Warren,  in  Boston. 
When  found,  its  posture  was  such  as  we  would  expect 
an  animal  to  have  that  sunk  in  mire.  Remains  of  its 
last  meal,  lying  between  its  ribs,  showed  that  it  lived,  in 
part  at  least,  on  spruce  and  fir-trees.  The  skeleton  is  11 
feet  high,  and  its  length  to  the  beginning  of  the  tail  is 
17  feet.  The  tusks  are  12  feet  long,  over  two  feet  of 
them  being  imbedded  in  the  bone  of  the  skull. 

Remains  of  a  mastodon  of  a  different  species  from  the 
North  American  one  have  been  found  in  South  America. 

409.  Mylodon. — In  the  pampean  or  prairie  formation 
of  South  America,  and  in  the  caves  of  Brazil,  have  been 
found  the  remains  of  certain  huge  animals  allied  to  the 
existing  Sloth  family.  There  are  only  three  species  of 
this  family  at  the  present  time,  and  they  are  of  moderate 
size ;  but  of  the  monsters  that  belonged  to  it  in  the  Post- 
tertiary  age  there  are  many  species.  Of  the  three  spe- 
cies of  one  genus,  Mylodon,  the  skeleton  of  one,  Mylodon 
robustus,  is  represented  in  Fig.  175.  The  sloths  of  the 
present  day  live  in  the  trees  of  dense  forests,  the  foliage 
being  their  food.  The  sloths  of  the  olden  time  lived  on 
the  same  kind  of  food,  as  is  shown  by  their  teeth ;  but 
they  were  too  heavy  to  climb,  and  they  obtained  the  fo- 
liage by  breaking  down  or  uprooting  trees.  In  doing 
this,  the  Mylodon  put  itself,  probably,  in  the  attitude  rep- 


AGE    OF    MAMMALS. 


299 


Fig.  175. 

resented  in  the  figure,  supporting  itself  on  its  two  hind 
legs  and  its  massive  tail,  as  on  a  tripod.  As  it  had  pow- 
erful claws,  it  undoubtedly  sometimes  dug  up  the  earth 
around  trees  preparatory  to  uprooting  them.  The  ani- 
mal was  of  about  the  size  of  a  rhinoceros  or  hippopota- 
mus. Its  skull  has  two  plates  of  bone  with  cells  between 
them,  as  is  the  case  with  the  skull  of  man ;  but  in  the 
mylodon  the  cellular  portion  is  very  large,  separating  the 
plates  of  bone  considerably.  The  reason  of  this  undoubt- 
edly is,  that  the  animal,  in  tearing  down  trees,  was  very 
liable  to  have  them  fall  down  upon  his  pate,  as  his  un- 
wieldy form  prevented  any  thing  like  nimble  efforts  in 
getting  out  of  harm's  way.  If  in  such  an  accident  the 
skull  were  fractured,  the  break  would  not  be  apt  to  ex- 


300  GEOLOGY. 

tend  beyond  the  cellular  portion  to  the  inner  plate  or 
table,  and  so  the  monster's  brain  would  be  safe,  suffering 
only  a  concussion,  from  which  it  would  speedily  recover. 
The  evidences  of  such  a  fracture  Professor  Owen  found 
in  one  skull,  and  they  were  such  as  to  show  that  the 
fracture  was  healed,  and  that  therefore  the  animal  sur- 
vived the  accident. 

410.  Megatherium. — This  animal  was  another  of  those 
Post-tertiary  South  American  sloths.  Its  name,  derived 
from  two  Greek  words,  megas,  great,  and  them,  wild 
beast,  indicates  its  enormous  bulk.  The  skeleton  of  one 
of  the  dozen  species  of  this  genus  is  represented  in  Fig. 
176.  The  length  of  this  animal  was  about  twelve  feet, 


Fig.l 


and  its  height  was  eight.  It  was  exceedingly  massive, 
its  thigh  bone  being  twice  as  thick  as  that  of  the  ele- 
phant, and  the  other  bones  are  in  like  proportion.  The 
width  of  the  tail  at  its  upper  part  was  two  feet.  Its 
fore  foot  was  more  than  three  feet  long,  and  one  foot  in 
width,  and  the  toes  were  armed  with  enormous  claws. 
It  lived  upon  leaves  and  twigs,  which  it  gathered  as  the 


AGE    OF   MAMMALS. 


301 


Mylodon  did,  by  pulling  down  trees,  as  represented  in 
the  case  of  one  species  in  the  front  part  of  Fig.  177. 


Fig.  1T7. 

Another  genus  of  the  Sloth-like  family  of  the  Post-terti- 
ary period  was  the  Megalonyx,  the  name  (megas,  great, 
and  onux,  nail)  being  given  to  it  on  account  of  its  large 
claws.  The  first  species  known  was  found  in  Virginia, 
and  this  name  was  suggested  by  President  Jeiferson. 
Its  size  was  about  that  of  an  ox,  but  it  was  much  more 
solidly  and  heavily  built. 

411.  Glyptodon. — This  genus,  embracing  several  spe- 


302  GEOLOGY. 

cies,  all  of  which  were  gigantic,  was  allied  to  the  arma- 
dilloes  of  the  present  day.  One  species  is  represented 
in  the  rear  part  of  Fig.  177.  This  animal  had  a  shell 
somewhat  like  a  turtle.  This  solid  coat  of  mail  is  com- 
posed of  innumerable  plates  joined  together  by  serrated 
or  notched  sutures.  Looked  at  from  within,  they  are 
hexagonal,  but  externally  they  form  a  mosaic  of  rosette- 
like  figures.  Remains  of  this  shell  were  first  found  in 
company  with  bones  of  the  megatherium,  and  were  sup- 
posed to  belong  to  that  animal.  But  the  truth  was  soon 
discovered  on  finding  an  entire  shell,  which  is  now  in  the 
museum  of  the  College  of  Surgeons  in  London.  This 
shell  is  nine  feet  in  length,  and  the  curve,  measured 
across,  is  seven  feet.  It  is  large  enough  to  cover  over  a 
large  number  of  the  armadilloes  of  the  present  day. 

412.  "Whales. — These  animals  appeared  in  localities  in 
the  Post-tertiary  period  far  away  from  their  present  hab- 
itats. The  sea  in  that  age  extended  up  as  an  arm  where 
the  St.  Lawrence  now  runs,  and  covered  the  present  lo- 
cality of  Lake  Champlain.  Whales  and  seals  flourished 
there  at  that  time,  and  their  remains  have  been  found 
among  other  spots  in  the  neighborhood  of  Montreal.  In 
Fig.  178  you  have  a  representation  of  the  bones  of  the 


Fig.  ITS. 

head  of  a  small  whale,  similar  to  the  existing  white 


AGE    OF   MAMMALS.  303 

whale  of  the  Northern  Sea,  as  they  were  dug  up  on  the 
borders  of  Lake  Champlain,  60  feet  above  its  waters, 
and  150  above  the  level  of  the  sea  at  the  present  time. 

413.  Kirkdale  Cave. — The  bones  of  animals  of  the 
Post-tertiary  age  have  been  found  to  some  extent  in 
caverns  in  Great  Britain,  on  the  Continent  of  Europe, 
and  in  Brazil,  in  South  America.  The  European  caves 
were  dens  of  cave-bears,  so  called  because  they  dragged 
their  prey  into  these  caves.  In  England  they  were  the 
dens  of  hyenas.  In  South  America  they  were  occupied 
by  wolves  and  certain  panther-like  animals.  The  most 
famous  cave  in  England  is  the  Kirkdale  Cave,  in  York- 
shire, the  mouth  of  which  was  accidentally  discovered 
by  some  workmen  in  1821,  in  quarrying  stone  on  the 
slope  of  a  limestone  hill.  I  transcribe  an  account  of  it 
given  by  Agassiz.  "  Overgrown  with  grass  and  bushes, 
the  mouth  of  this  cave  in  the  hill-side  had  been  effectual- 
ly closed  against  all  intruders,  and  it  was  not  strange 
that  its  existence  had  never  been  suspected.  The  hole 
was  small,  but  large  enough  to  admit  a  man  on  his  hands 
and  knees ;  and  the  workmen,  creeping  in  through  the 
opening,  found  that  it  led  into  a  cavern,  broad  in  some 
parts,  but  low  throughout.  There  were  only  a  few  spots 
where  a  man  could  stand  upright ;  but  it  was  quite  ex- 
tensive, with  branches  opening  out  from  it,  some  of 
which  have  not  yet  been  explored.  The  whole  floor 
was  strewn,.from  one  end  to  the  other,  with  hundreds 
of  bones,  like  a  huge  dog-kennel.  The  workmen  won- 
dered a  little  at  their  discovery,  but,  remembering  that 
there  had  been  a  murrain  among  the  cattle  in  this  re- 
gion some  years  before,  they  came  to  the  conclusion  that 
these  must  be  the  bones  of  cattle  that  had  died  in  great 
numbers  at  that  time,  and,  having  so  settled  the  matter 
to  their  own  satisfaction,  they  took  little  heed  to  the 
bones,  but  threw  many  of  them  out  on  the  road  with  the 
common  limestone.  Fortunately,  a  gentleman  living  in 
the  neighborhood,  whose  attention  had  been  attracted 


304  GEOLOGY. 

to  them,  preserved  them  from  destruction ;  and  a  few 
months  after  the  discovery  of  the  cave,  Dr.  Buckland, 
the  famous  English  geologist,  visited  Kirkdale  to  exam- 
ine its  strange  contents,  which  proved,  indeed,  stranger 
than  any  one  had  imagined,  for  many  of  these  remains 
belonged  to  animals  never  before  found  in  England.  The 
bones  of  hyenas,  tigers,  elephants,  rhinoceroses,  and  hip- 
popotamuses were  found  mingled  with  those  of  deer, 
bears,  wolves,  foxes,  and  many  smaller  creatures.  The 
bones  were  gnawed,  and  many  were  broken,  evidently 
not  by  natural  decay,  but  seemed  to  have  been  snapped 
violently  apart.  After  the  most  complete  investigation 
of  the  circumstances,  Dr.  Buckland  convinced  himself, 
and  proved  to  the  satisfaction  of  all  scientific  men,  that 
the  cave  had  been  a  deu  of  hyenas  at  a  time  when  they, 
as  well  as  tigers,  elephants,  rhinoceroses,  etc.,  existed  in 
England  in  as  great  numbers  as  they  now  do  in  the  wild- 
est parts  of  tropical  Asia  or  Africa.  It  was  evident  that 
the  hyenas  were  the  lords  of  this  ancient  cavern,  and  the 
other  animals  their  unwilling  guests,  for  the  remains  of 
the  latter  were  those  which  had  been  most  gnawed,  bro- 
ken, and  mangled ;  and  the  head  of  an  enormous  hyena, 
with  gigantic  fangs,  found  complete,  bore  ample  evidence 
to  their  great  size  and  power.  Some  of  the  animals,  such 
as  the  elephants,  rhinoceroses,  etc.,  could  not  have  been 
brought  into  the  cave  without  being  first  killed  and  torn 
to  pieces,  for  it  is  not  large  enough  to  admit  them.  But 
their  gnawed  and  broken  bones  attest,  nevertheless,  that 
they  were  devoured  like  the  rest ;  and,  probably,  the  hy- 
enas then  had  the  same  propensity  which  characterizes 
those  of  our  own  time,  to  tear  in  pieces  the  body  of  any 
dead  animal,  and  carry  it  to  their  den,  to  feed  upon  it 
apart." 


AGE   OF   MAN.  305 


CHAPTER  XIX. 

AGE   OF  MAN. 

414.  Boundaries  of  this  Age. — In  the  ages  of  the  far 
past,  as  you  have  already  seen,  there  is  no  exact  line  di- 
viding one  age  from  another.     So  it  is  with  the  present 
age,  and  the  Post-tertiary  that  preceded  it.    It  has  been 
the  common  idea  that  the  advent  of  man  is  fixed  by  the 
chronology  of  the  Bible  at  about  6000  years  ago,  and 
the  researches  of  geology  have  been  thought  to  coincide 
with  this ;  but  recently  there  have  been  some  researches 
which  seem  to  put  the  introduction  of  man  farther  back 
than  this.     The  question  is  yet  undecided,  but  if  the  re- 
sult indicated  should  be  arrived  at  definitely,  it  would 
not  show  that  the  Bible  is  false,  as  some  would  have  it, 
but  merely  that  the  common  view  of  its  early  chronolo- 
gy is  wrong.     As  to  the  conclusion  of  the  present  age, 
geology  leaves  us  entirely  in  the  dark.     The  Bible  does 
indeed  point  to  a  time  when  the  affairs  of  this  world 
shall  be  concluded,  and  the  earth  cease  to  be  the  habita- 
tion of  the  human  race,  a  vast  change  being  indicated 
by  the  announcement  that  "  the  heavens  shall  pass  away 
with  a  great  noise,  and  the  elements  shall  melt  with  a 
fervent  heat;  the  earth  also,  and  the  works  that  are 
therein,  shall  be  burned  up."     But  the  geologist,  though 
he  sees  in  the  operations  that  are  now  going  on  eviden- 
ces of  great  future  changes  in  the  arrangement  of  the 
earth's  surface,  finds  nothing  which  could  enable  him  to 
predict  any  such  radical  change  as  the  Bible  plainly, 
though  in  general  and  indefinite  terms,  points  out. 

415.  Earth  now  and  in  Former  Ages.  —  The  contrast 
between  the  state  of  the  earth  in  the  present  age  and  in 
any  of  the  former  ages  is  very  great,  and  the  farther  we 


306  GEOLOGY. 

go  back  in  the  comparison  the  more  striking  does  it  ap- 
pear. To  say  nothing  of  that  period  or  age  when  the 
earth  was  in  a  fused  condition,  look  at  the  Azoic  age 
as  compared  with  the  present.  When  the  extent  of 
land  was  small,  and  there  was  no  life  either  on  land,  or 
in  water,  or  air,  there  were  no  high  mountains,  and  no 
rivers  of  any  size.  It  was  a  dull,  monotonous  world, 
compared  with  the  variegated  earth  which  we  have  now, 
with  its  continents,  islands,  mountains,  lakes,  and  rivers, 
all  swarming  with  busy  and  noisy  life.  A  strong  con- 
trast can  be  made  out  in  regard  to  the  ages  that  follow- 
ed, especially  in  relation  to  the  changes  of  various  kinds 
that  were  necessary  in  making  the  requisite  additions  to 
the  continents,  such  .as  flexures,  upheavals,  denudations, 
deposits,  elevations,  subsidences,  etc.  Disturbances,  it  is 
true,  are  occurring  in  this  age,  many  of  them  precisely  of 
the  same  character ;  but  they  are  not  so  great,  nor  so 
wide  in  their  range.  For  example,  glaciers  and  icebergs 
are  at  work  now;  but  their  work  is  not  continent-wide, 
as  it  was  in  the  Glacial  age,  when  ice  reigned  supreme 
over  a  large  portion  of  the  earth,  in  order  to  prepare  it, 
as  you  have  seen,  for  man.  So,  in  the  formation  of  peat, 
we  have  the  same  thing  essentially  as  was  the  grand 
business  of  the  Carboniferous  age ;  but  it  is  a  small  op- 
eration compared  with  the  coal-making  of  that  period. 
The  Post-tertiary  period  was  the  nearest  in  character  to 
the  present,  especially  the  Terrace  epoch,  for  the  conti- 
nents were  then  finished,  and  all  the  grand  general  work 
of  diversification  of  the  surface  was  completed,  only  the 
minor  diversification,  as  it  may  be  termed,  remaining  to 
be  done. 

416.  Completion  of  the  Earth. — Although  changes,  and 
those  of  no  small  extent,  are  now  going  on  in  the  crust 
of  the  earth,  yet,  in  a  certain  sense,  it  may  be  regarded 
as  having  been  completed  at  the  time  when  man  was  in- 
troduced upon  it.  This  conclusion  is  seen  to  be  true  if 
we  consider  certain  prominent  facts,  viz.,  that  the  conti- 


AGE    OF    MAN.  307 

nents  had  their  germs,  and  grew  gradually  by  accretions, 
after  a  regular  plan,  to  their  present  dimensions ;  that 
after  their  proper  size  was  reached  great  operations  were 
instituted  to  diversify  the  surface,  and  to  grind  up  some 
of  the  rocks  into  soil  for  the  use  of  man  ;  that  the  prep- 
arations of  the  earth's  crust,  even  down  to  minute  cir- 
cumstances, so  far  as  they  are  understood,  can  be  seen 
to  look  toward  the  consummation  arrived  at  in  the  age 
of  Man ;  and,  finally,  that  man,  appearing  after  a  succes- 
sion of  animals  extending  through  long  ages,  differs 
from  them  all  in  the  possession  of  qualities  that  ally  him 
with  the  Infinite,  and  therefore  show  him  to  be  the  fit- 
ting end  of  such  a  consummation.  The  earth  was  made 
for  man.  Accordingly,  he  has  a  general  control  over 
the  powers  of  earth,  being  commissioned  "  to  subdue  it, 
and  have  dominion  over  the  fish  of  the  sea,  and  over  the 
fowl  of  the  air,  and  over  every  living  thing  that  moveth 
upon  the  earth."  Mind  gives  him  this  control,  even 
where  physical  circumstances,  as  weight  and  strength  of 
muscle,  are  sufficient  to  overpower  him  in  any  direct  ef- 
fort. He  is  the  lord  of  this  lower  creation,  acting  as  the 
vicegerent  of  the  Creator. 

417.  Changes  now  Transpiring. — The  changes  which 
have  taken  place  during  the  age  of  Man,  and  are  now 
going  on,  have  been  quite  fully  noticed  in  Chapter  X., 
and  I  shall  only  give  a  summary  of  them  here.  The 
rocks  are  every  where  subjected  to  weathering,  which 
wears  them  away  by  piecemeal,%nd  the  rivers  are  car- 
rying away  the  detritus  of  the  rocks,  lodging  it  in  deltas 
or  on  flood-plains.  The  tendency  of  all  this  is  to  fill  up 
the  depressions,  and  to  make  the  land  encroach  upon  the 
space  occupied  by  the  water.  Then  there  is  evidence 
that  over  extensive  areas  of  the  floor  of  the  sea  deposits 
are  being  laid  down  of  the  same  materials  that  now  com- 
pose rocks  made  in  former  ages.  Besides,  there  are  the 
coral  animals  busily  engaged  in  building  extensive  reefs. 
There  is,  therefore,  great  land-building  going  on,  and  the 


308  GEOLOGY. 

result  must  inevitably  be,  that  the  level  of  the  ocean  will 
rise,  unless  there  be  some  movements  of  the  land  to  coun- 
teract it.  Elevations  in  the  land  or  depressions  in  the 
floor  of  the  sea  would  do  this.  That  elevations  have 
occurred  within  this  age,  and  are  occurring  now,  we 
have  the  clearest  evidence,  as  shown  in  Chapter  X.  It 
may  be  that  the  heaving  of  volcanoes,  adding  to  the 
land,  may  occasion  some  corresponding  depressions  in 
the  floor  of  the  sea  in  their  neighborhood.  At  any  rate, 
in  some  way  the  general  level  of  the  ocean  in  relation  to 
the  land  is  maintained  about  the  same  from  century  to 
century.  The  preservation  of  this  equilibrium  in  the 
midst  of  constant  changes  is  secured  by  the  same  all- 
wise  and  all-powerful  Providence  that  preserves  the  uni- 
versal constitution  of  the  atmosphere,  as  noticed  in  §  85, 
Part  II.  This  appears  very  wonderful  when  we  reflect 
that  the  earth  is  essentially  a  molten  ball  covered  with  a 
hard  crust,  which  has  vent-holes  communicating  with  the 
internal  fires,  and  contains  vast  quantities  of  water  in  its 
depressions. 

418.  Present    Activity    of   the    Agencies    Producing 
Change. — The  causes  of  the  present  changes  in  the  earth 
were  brought  to  view  in  §  172,  and  were  there  stated  to 
be  the  same  as  have  been  in  action  in  the  different  ages 
of  the  earth's  formation.     All  of  them  have  been  in  op- 
eration from  the  first  except  one,  that  is,  life,  which  was 
introduced  upon  the  stage  after  the  long  periods  of  the 
Azoic  age  were  passed?    An  interesting  question  arises 
in  regard  to  the  degree  of  activity  of  these  agencies  at 
the  present  time.    Lyell  and  some  others  claim  that  they 
are  as  active  now  as  they  ever  were ;  but  the  evidences 
in  favor  of  the  opposite  opinion  are  very  decisive.    They 
surely  are  not  as  strongly  at  work  now  as  they  were 
when  they  raised  up  the  lofty  mountains,  or  when,  in  the 
Azoic  age,  the  crust  of  the  earth  was  solidifying  at  the 
first,  and  the  germs  of  the  continents  were  forming. 

419.  Historic  and  Human  Periods. — What  is  called  the 


AGE    OF   MAN.  309 

Human  period  covers  the  whole  age  of  Man,  but  the  His- 
toric period  does  not.  What  purports  to  be  the  early 
history  of  many  of  the  old  nations  is  made  up  of  tradi- 
tions, which  are  far  from  being  reliable.  Real  history, 
with  the  exception  of  the  inspired  history  of  the  Bible, 
goes  but  a  little  way  back  in  the  case  of  any  ancient  na- 
tion. "  Milton  did  not  scruple  to  declare,"  says  Hume, 
"  that  the  skirmishes  of  kites  or  crows  as  much  merited 
a  particular  narrative  as  the  confused  transactions  and 
battles  of  the  Saxon  Heptarchy."  But  the  study  of  the 
remains  of  a  people  may  be  carried  far  back  into  the 
past,  beyond  the  beginning  of  that  degree  of  civilization 
which  is  necessary  to  authentic  history,  and  may  give  us 
valuable  results.  It  is  by  such  study  alone  that  we  can 
acquire  a  knowledge  of  ancient  nations  in  their  savage 
or  barbaric  state. 

420.  Stone,  Bronze,  and  Iron  Ages  of  Man. — In  mark- 
ing the  progress  of  man  by  means  of  the  remains  of  his 
implements,  weapons,  ornaments,  etc.,  the  materials 
which  he  has  used  in  making  them  have  been  consid- 
ered as  denoting  three  stages.  In  the  first  and  rudest 
condition  we  have  the  Stone  age,  when  stone  was  the 
material  from  which  were  shapen  such  implements  as 
hammers,  axes,  chisels,  and  arrow-heads.  In  Fig.  179  (p. 
310)  are  represented  some  of  these  early  stone  imple- 
ments gathered  from  various  quarters,  all  of  them  exhib- 
iting a  striking  similarity,  but  some  of  them  being  a  lit- 
tle more  elaborate  than  the  others.  Those  at  1  and  2 
are  from  the  Valley  of  the  Somme,  in  France ;  at  3,  4, 
and  5,  from  England ;  at  6,  7,  and  8,  from  Canada ;  and 
at  9  and  10,  from  Scandinavia.  Quite  an  advance  upon 
this  is  the  Bronze  age,  for  there  are  more  thought  and 
skill  shown  in  melting  metals  together  for  the  making 
of  implements  than  in  the  bare  shaping  of  stone.  Cop- 
per was  the  chief  metal  of  this  age.  Last  of  all  comes 
the  Iron  age,  in  which  the  excellence  of  iron  above  all 
other  metals  for  the  manufacture  of  tools  and  weapons  is 


310 


GEOLOGY. 


Fig.  179. 

recognized,  the  advance  in  thought  and  contrivance  hav- 
ing enabled  man  to  discover  the  art  of  preparing  it,  by 
various  smelting  processes,  for  this  purpose.  It  is  curious 
to  notice  how  each  of  these  ages  has  its  peculiar  style 
of  ornaments,  dwellings,  etc.  There  is  no  literature,  and 
therefore  no  history,  in  so  rude  a  condition  as  that  of  the 
Stone  age,  and  almost  none  in  the  Bronze;  but  when  a 
nation  or  tribe  is  so  far  advanced  in  the  arts  as  to  work 
iron,  there  is  a  literature,  small  at  first,  but  increasing 
with  every  advance  in  the  arts  of  civilization. 

421.  Animals. — In  the  age  just  previous  to  the  age  of 
Man  brute  force  held  sway  in  the  animal  kingdom.  It 
was  fitting,  therefore,  that  as  the  reign  of  intellect  in  the 
world  was  ushered  in,  such  monsters  as  the  megatheri- 
ums, mammoths,  mastodons,  etc.,  should  drop  out  of  ex- 
istence, and  that  the  animals  so  useful  to  man,  and  so 
easily  controlled  by  him,  as  the  ox,  the  horse,  the  sheep, 
etc.,  should  appear  upon  the  earth  in  such  abundance. 
The  line  of  separation  between  this  and  the  Terrace  pe- 
riod in  regard  to  animals  is  not  a  fixed  and  definite  one. 
It  is  not  so  even  in  regard  to  the  Mammalia.  Some  ex- 
isting now  began  their  existence  in  the  Terrace  period, 


AGE    OF   MAN.  311 

but  there  is  a  difference  of  opinion  as  to  how  many  of 
them  did  so.  There  are  more  of  insects  and  birds  in  the 
present  age  than  in  any  previous  one,  but  not  so  many 
mammals  as  in  the  Mammalian  age,  or  reptiles  as  in 
the  Reptilian  age.  Some  animals  have  become  extinct 
within  the  memory  of  man.  Outlines  of  three  of  them 
are  given  in  Fig.  180  (p.  312).  The  shortest  one,  the 
Dodo,  which  lived  in  Mauritius  and  other  adjoining  isl- 
ands, was  a  heavy,  clumsy  bird,  covered  with  loose, 
downy  feathers,  and  having  imperfect  wings.  It  weighed 
about  fifty  pounds.  The  earlier  voyagers  saw  it,  and 
made  sketches  of  it;  but  after  the  possession  of  the  isl- 
and of  Mauritius  by  the  French  in  1712  it  was  no  longer 
known,  and  one  or  two  heads  and  feet  of  this  bird  are 
all  that  remain  of  it  in  the  cabinets  of  Europe.  The  tall- 
est figure  is  an  outline  of  the  Dinornis  elephantoides  of 
New  Zealand,  exceeding  the  ostrich  in  size.  The  name 
comes  from  two  Greek  words,  demos,  terrible,  and  ornis, 
bird.  The  outline  on  the  right  represents  another  spe- 
cies, the  Dinornis  ingens.  Bones  have  been  found  in 
Madagascar  similar  to  those  of  these  birds,  and  quite  as 
large,  and  with  them  some  egg-shells.  The  bird  to 
which  they  belonged  has  been  called  ^Epiornis  maxi- 
mus.  Its  egg  was  over  a  foot  in  diameter,  and  equaled 
148  hen's  eggs  and  50,000  humming-bird's  eggs  in  size. 
422.  Man  One  Species. — Although  some  few  physiolo- 
gists hold  an  opposite  opinion,  the  evidence  is  very  de- 
cided that  all  the  varieties  of  the  human  race  belong  to 
one  species,  as  is  declared  in  the  Bible.  As  this  evi- 
dence is  brought  out  quite  fully  in  my  "  Human  Physiol- 
ogy," I  will  not  go  into  details  here.  Suffice  it  to  say 
now,  that  the  resemblance,  we  may  say  identity,  of  the 
races  of  men  in  all  essential  physical  characteristics,  and 
especially  in  those  which  are  mental,  is  unmistakable, 
and  that  all  the  varieties  can  be  accounted  for  from  the 
influence  of  circumstances,  which,  indeed,  acting  also 
upon  other  animals  inferior  to  man,  but  every  where  ac- 


GEOLOGY. 


Fig.  ISO. 

companying  him,  as  dogs,  horses,  etc.,  have  produced  in 
them  somewhat  similar  results. 

423.  Man's  Place  in  Nature.— The  grand  difference  be- 


AGE    OF   MAN.  313 

tween  man  and  other  animals  is  one  of  kind,  and  not  of 
degree  only.  He  is  not  merely  the  highest  of  a  series 
of  animals,  as  some  assert,  but  he  possesses  certain  qual- 
ities that  do  not  belong  in  any  degree  to  the  animals  be- 
low him.  He  stands  in  some  respects  alone.  In  phys- 
ical structure  he  is,  indeed,  allied  to  other  animals,  be- 
cause he  lives  amid  the  same  material  circumstances, 
and  has  similar  bodily  wants.  These  relations  with  oth- 
er things  make  it  also  necessary  that  he  should  have 
similar  instincts,  and,  to  some  extent,  similar  thoughts 
and  reasonings,  for  brutes  do  have  a  lower  order  of 
reasoning — that  is,  they  draw  simple  inferences.  But 
here  the  resemblance  stops.  There  is  a  certain  depart- 
ment of  mind  which  belongs  exclusively  to  man,  and  sep- 
arates him  by  an  impassable  gulf  from  other  animals.  It 
is  the  power  of  abstract  or  general  reasoning  that  distin- 
guishes the  mind  of  man  from  that  of  the  brute.  No 
brute,  however  much  he  may  know,  can  ever  himself 
either  discover,  or  receive  by  instruction,  any  general 
principle.  It  is  this  power  that  gives  man  the  knowl- 
edge of  the  existence  of  a  great  First  Cause,  and  of  the 
difference  between  right  and  wrong,  and  that  introduces 
him  into  a  sphere  of  thought  and  feeling  which  he  occu- 
pies in  common  with  the  angels,  and  with  the  Creator 
himself.  It  is  this  which  makes  him  " a  living  soul"  It 
is  from  this  that  he  is  said  to  be  created  in  the  image  of 
God.  From  this  come  all  his  endless  contrivance  in  im- 
plements and  machinery,  his  attainments  in  science,  and 
his  construction  of  language.  This  subject,  thus  briefly 
noticed  here,  is  fully  treated  in  my  "  Human  Physiology." 
424.  A  Supposition. — It  is  the  idea  of  some  that,  as 
man  is  the  present  culmination  of  the  animal  kingdom, 
there  is  still  to  be  an  onward  progress,  and  that  some 
other  being  of  a  higher  order  even  than  man  will,  after 
a  while,  appear  upon  the  scene.  There  would  be  some 
reason  for  this  expectation  if  there  had  been  a  regular 
gradation  from  the  first  dawn  of  life  in  the  Silurian  age, 

O 


314  GEOLOGY. 

evolving  man  at  last  at  the  summit  of  the  series,  the  dif- 
ference between  him  and  the  highest  of  other  animals 
being  only  in  degree.  But  there  is  no  such  regularity 
of  gradation,  and  man  is  not  merely  the  highest  in  grade 
of  all  animals,  but  he  differs  from  them  in  the  possession 
of  mental  attributes,  that  ally  him  with  the  Infinite,  and 
force  upon  us  the  conviction  that  the  earth  was  made  for 
him,  and  that  he  alone  is  the  end  of  its  creation. 


CHAPTER  XX. 

CONCLUDING    OBSERVATIONS. 

425.  Geology  and  Astronomy  Compared. — In  Astrono- 
my we  take  into  consideration  systems  of  planets  which 
are  at  immense  distances  from  each  other,  but  in  Geol- 
ogy our  view  is  confined  to  a  single  planet,  and  that  a 
comparatively  small  one.  In  the  study  of  Astronomy 
we  have  only  the  vast  and  the  grand  before  us,  and 
there  is  nothing  small,  or  even  moderate  in  size,  much 
less  minute ;  but  in  Geology  we  have  a  combination  of 
the  vast  and  the  small,  so  that  the  study  has  more  of 
the  elements  of  interest  in  it  than  Astronomy  presents. 
While  conceptions  of  grandeur  are  sufficiently  awaken- 
ed by  some  of  the  extended  movements  of  continent- 
making,  much  of  the  subject  lies  directly  under  our  feet, 
and  invites  the  most  familiar  examination.  The  interest 
is  enhanced  when  we  see  that  even  operations  so  minute 
as  to  call  for  the  microscope  in  their  investigation  have 
been  concerned  in  laying  down  strata  of  immense  extent 
and  thickness,  in  the  building  up  of  continents,  and  that 
these  operations  are  in  some  degree  still  going  on.  Be- 
sides, the  fact  that  it  is  our  earth  that  we  examine  in 
its  vast  stony  leaves — that  all  those  multiform  processes 
which  have  occupied  long  ages  were  constructing  a  hab- 
itation for  us,  gives  to  the  study  an  interest  which  does 
not  attach  to  the  study  of  other  planets. 


CONCLUDING    OBSERVATIONS.  315 

426.  Record  of  the  Rocks  and  History.  —  In  reading 
history  as  written  by  men  there  is  always  more  or  less 
doubt  about  its  reliability.     It  is  even  so  with  the  histo- 
ry of  recent  times,  but  more  especially  with  that  of  times 
long  gone  by,  as  already  alluded  to  in  §  419;  but  the 
record  which  the  Creator  has  left  in  the  rocks  is  a  true 
history.     When  Geology  first  unfolded  its  leaves  to  the 
world,  it  was  the  idea  of  some  that  the  animal  and  vege- 
table forms  found  in  the  strata  were  the  mere  images  of 
living  things  imprinted  there,  and  not  actual  remains. 
This  most  unworthy  idea  of  the  Deity's  work  of  creation 
is  not  now  entertained  by  any  one,  but  the  history  folded 
up  in  the  rocks  is  universally  recognized  as  a  true  life- 
record  of  past  ages.    We  may  sometimes  err  in  read' 
ing  it,  or  may  even  fail  to  decipher  it ;  but,  nevertheless, 
there  is  no  mistake  in  this  record  written  by  the  Infinite 
and  the  True. 

427.  The  Two  Divine  Records  of  the  Creation. — There 
are  two  authentic  records  of  the  creation  of  the  earth, 
the  one  contained  in  the  Bible,  and  the  other  inscribed 
on  the  rocks.    Some  scientific  men,  who  do  not  absolute- 
ly deny  the  truth  of  the  Bible,  seem  to  think  that  the 
record  developed  by  their  discoveries  has  a  certain  and 
indisputable  claim  on  their  faith,  which  the  other  record 
has  not.     But  both  are  equally  authentic,  though  the  ev- 
idences of  authenticity  are  different  in  the  two  cases.    It 
is  just  as  well  established  that  the  Bible  is  a  divine  rec- 
ord, the  authors  being  merely  agents  of  the  Deity,  as 
that  the  record  in  the  rocks  was  made  by  divine  power, 
heat,  water,  light,  electricity,  etc.,  being  the  agents  by 
which  it  was  made.     These  two  records  can  not,  then, 
be  inconsistent  with  each  other,  though  they  may  be  ap- 
parently so,  from  a  wrong  interpretation  of  the  one  or 
the  other.    In  interpreting  the  account  of  the  earth's  cre- 
ation in  the  Bible,  we  must  remember  that  it  does  not 
purport  to  be  a  scientific  account,  and  therefore  common, 
and  not  scientific  expressions  are  used.     Judged  of  in  a 


316  GEOLOGY. 

reasonable  manner,  it  is  plain  that  this  account,  which  is 
so  universally  admired  for  its  sublimity,  has  remarkable 
coincidences  with  the  record  in  the  rocks.  These  have 
been  admirably  traced  out  by  Hugh  Miller,  Dana,  and 
others,  and  I  will  not  dwell  upon  them  here.  They  are 
such  that  every  candid  mind  must  conclude,  in  view  of 
them,  with  Dana,  that  "  no  human  mind,  in  the  early  age 
of  the  world,  unless  gifted  with  superhuman  intelligence, 
could  have  contrived  such  a  scheme."  It  might  have 
been  done  by  some  very  wise  man  of  the  present  time, 
with  the  aid  of  all  the  knowledge  which  the  researches 
of  Geology  could  give  him,  though  not  with  such  re- 
markable skill  and  sublimity ;  but  to  do  it  previous  to 
the  acquisition  of  this  knowledge  would  be  an  impossi- 
bility. The  conclusion,  then,  is  inevitable,  that  Moses 
was  guided  by  superhuman  power  in  making  the  ac- 
count, or,  in  other  words,  was  divinely  inspired. 

Many  geologists  think  it  out  of  place  to  notice  at  all 
the  record  in  the  Bible ;  but  if  it  be  true  that  the  Deity 
has  given  us  a  written  record,  it  is  our  duty  to  examine 
it  thoroughly  and  candidly,  and  a  reasonable  reference 
to  it  in  a  scientific  work  can  not  be  out  of  place.  It  is 
the  dictate  of  science  as  well  as  religion  to  notice  it,  and 
therefore  it  is  done  by  such  eminent  men  as  Dana,  Hitch- 
cock, Hugh  Miller,  etc. 

428.  The  Days  in  the  Mosaic  Record. — That  the  days 
which  Moses  says  were  occupied  by  the  Creator  in  the 
creation  were  long  ages  is  evident  from  a  comparison  of 
the  order  of  events  in  that  narrative  with  that  revealed 
by  the  record  of  the  rocks.  But  perhaps  it  is  objected 
that  the  plain  reading  of  the  account  would  lead  any  one 
to  believe  that  the  six  days  of  the  creation  were  days  of 
twenty-four  hours  each.  So  it  would,  if  not  interpreted 
by  the  knowledge  which  Geology  has  given  us,  just  as 
we  should  infer  from  the  language  of  the  Bible  that  the 
sun  actually  rises  and  sets,  as  the  ecclesiastical  court  that 
imprisoned  Galileo  believed,  until  Astronomy  taught  us 


CONCLUDING    OBSERVATIONS.  317 

otherwise.  In  regard  to  the  word  day,  we  continually 
use  it  in  various  senses,  and  Dana  states  that  it  is  used 
in  five  different  senses  in  the  Mosaic  account  of  the  cre- 
ation. "  <  These  are,'  he  says,  (1 .)  The  light—'  God  called 
the  light  day,'  v.  5 ;  (2.)  the  '  evening  and  the  morning' 
before  the  appearance  of  the  sun;  (3.)  the  'evening  and 
the  morning'  after  the  appearance  of  the  sun ;  (4.)  the 
hours  of  light  in  the  twenty-four  hours  (as  well  as  the 
whole  twenty-four  hours),  in  verse  14 ;  and,  (5.)  in  the  fol- 
lowing chapter,  at  the  commencement  of  another  record 
of  creation,  the  whole  period  of  creation  is  called '  a  day.' 
The  proper  meaning  of '  evening  and  morning'  in  a  his- 
tory of  creation  is  beginning  and  completion;  and  in 
this  sense  darkness  before  light  is  but  a  common  meta- 
phor." It  is  a  significant  fact,  I  add,  that  the  word  day 
is  applied  to  the  three  first  periods  of  creation,  when  as 
yet  the  sun  had  not  appeared.  There  could  have  been 
then  no  such  division  as  our  day ;  and,  indeed,  it  is  ex- 
pressly stated  that  this  division  was  introduced  in  the 
fourth  period  or  day  of  creation,  for  it  is  said  of  the 
lights  in  the  firmament,  "  Let  them  be  for  signs,  and  for 
seasons,  and  for  days,  and  years." 

429.  Traditions  and  Superstitions. — There  have  been 
many  traditions  and  superstitions  in  regard  to  creation, 
and  the  origin  of  various  fossils  that  were  accidentally 
found  in  the  rocks  before  geology  was  knowu  as  a  sci- 
ence. I  have  here  and  there  referred  to  some  of  these. 
There  is  an  interesting  English  legend  in  regard  to  fos- 
sil ammonites.  These  abound  in  the  neighborhood  of 
Whitby,  in  Yorkshire,  and  it  was  a  common  belief  there 
that  they  are  petrified  snakes.  The  story  of  their  petri- 
faction is  this :  As  the  snakes  were  so  numerous  as  to 
prove  a  great  annoyance  to  the  inhabitants,  they  im- 
plored their  patron  saint,  St.  Hilda,  to  intercede  for  their 
destruction,  whereupon  she  not  only  prayed  their  heads 
off,  but  prayed  them  also  into  stone.  Sir  Walter  Scott 
thus  records  the  legend  in  his  Marmion  : 


318  GEOLOGY. 

"  And  how  the  nuns  of  Whitby  told 
How,  of  countless  snakes,  each  one 
Was  changed  into  a  coil  of  stone 
When  holy  Hilda  prayed. 
Themselves  within  their  sacred  bound, 
Their  stony  folds  had  often  found." 

So  lately  was  this  superstition  current,  that  the  author 
of  a  modern  scientific  work  relates  that  a  sharp  dealer, 
who  was  requested  by  his  customers  to  supply  them 
with  some  of  the  creatures  that  had  escaped  that  part 
of  St.  Hilda's  prayer  which  de- 
stroyed their  heads,  affixed  to 
the  fossils  some  heads  of  plaster 
of  Paris  suitably  colored.  He 
had  a  thriving  trade  till  it  was 
upset  by  some  officious  geolo- 
gist. But  even  now  the  fossils 
are  sold  in  Whitby  with  the  ex- 
tremity of  the  last  whorl  filed 
into  the  shape  of  a  snake's  head, 
Fis-181-  as  represented  in  Fig.  181. 

430.  Use  of  Geology  to  the  Poet  and  the  Painter. — Ge- 
ology is  of  service  to  the  poet  in  adding  largely  to  his 
fund  of  facts  such  as  are  eminently  fitted  to  awaken  the 
sublimest  thoughts  and  feelings,  and  to  give  a  wide  range 
to  the  flights  of  his  imagination.     It  is  of  use  to  the  paint- 
er of  scenery  as  anatomy  is  to  the  painter  of  the  human 
form,  for  it  gives  us,  as  we  may  say,  the  anatomy  of  the 
earth.     Besides,  it  supplies  him  with  many  valuable  and 
interesting  hints  as  to  the  objects  upon  the  earth's  surface. 

431.  Plan  in  Earth-development. — You  have  seen,  in 
the  course  of  your  study  in  this  book,  that  the  Creator 
worked  from  the  beginning  after  a  plan,  in  developing 
the  continents  on  the  crust  of  the  earth,  and  if  we  could 
go  down  into  the  depths  of  the  ocean,  and  examine  the 
irregularities  of  its  floor,  we  should  undoubtedly  see  the 
same  thing  there.     What  the  geologist  has  shown  us  in 


CONCLUDING    OBSERVATIONS.  319 

regard  to  this  plan  is  like  what  we  see  as  we  look  upon 
a  potter  as  he  makes  some  vessel.     We  see  the  general 
plan  developed  very  soon  after  he  begins  to  turn  the  ball 
of  clay,  and  the  minutiae  of  the  plan  appear  more  and 
more  as  he  proceeds.     Just  so  the  investigations  of  geol- 
ogists have  shown  how  the  continents,  at  the  very  com- 
mencement of  their  formation,  had  a  shape  which  looked 
toward  what  they  now  are,  and  how  they  were  gradual- 
ly developed,  and  at  length  were  finished  in  all  the  mi- 
nutiae of  their  diversification.     And  I  may  remark  here 
that  each  continent  had  its  own  plan.     While,  for  exam- 
ple, the  North  American  continent,  as  you  saw  in  §  267, 
began  with  the  formation  of  one  long  island,  Europe  was 
at  first  a  group  of  islands,  which  were  afterward  united 
together.     There  was  a  plan,  also,  in  regard  to  the  ani- 
mals of  the  earth.     This  is  seen  in  the  preservation  of 
the  four  grand  divisions  of  animals  from  the  beginning, 
through  all  the  changes  of  genera  and  species;  in  the 
gradual  advance  from  the  lower  up  to  the  higher  forms, 
through  the  ages  of  the  earth's  growth ;  in  the  introduc- 
tion of  particular  forms  for  special  purposes,  at  certain 
periods,  and  in  certain  localities;  and  in  the  final  con- 
summation of  the  animal  kingdom,  in  which,  after  all  its 
long  line  of  successions,  there  was  an  adaptation  of  it  to 
the  wants  of  man,  who  was  constituted  its  ruler.     The 
same  may  be  substantially  said  of  the  vegetable  kingdom. 
432.  Time  in  Geological  Processes.  —  I  have  here  and 
there,  in  previous  chapters,  given  some  illustrations  of  the 
great  lengths  of  time  required  for  the  formation  which 
make  up  the  crust  of  the  earth.     You  will  recollect  the 
calculation  of  Liebig,  noticed  in  §  318,  in  regard  to  the 
formation  of  coal.     Calculations  have  also  been  made  in 
regard  to  the  deposition  of  the  strata  of  rocks,  and  the 
estimates  for  all  the  formations,  from  the  Azoic  down, 
reach  a  sum  total  of  over  fifty  million  of  years.     The  es- 
timates are  based  upon  the  rate  at  which  rocks  are  de- 
posited and  solidified  in  lakes  and  seas  at  the  present 


320  GEOLOGY. 

time.  There  is  nothing  in  science  which  so  well  im- 
presses the  mind  with  the  truth  of  the  declaration  of  the 
Bible,  that  "  one  day  is  with  the  Lord  as  a  thousand 
years,  and  a  thousand  years  as  one  day." 

433.  Minute  Agencies. — I  have  brought  to  your  notice 
in  this  book  many  examples  of  extensive  operations  in 
the  construction  of  the  earth  by  minute  agencies.     It  is 
a  very  small  thing  for  a  coral  animal  to  separate  from 
the  water  a  little  carbonate  of  lime  and  appropriate  it  to 
itself;  but  multitudes  of  these  animals,  at  work  in  the 
same  locality,  year  after  year,  for  centuries  and  even 
ages,  lay  down  thick  masses  of  limestone  rock.    The  case 
is  even  stronger  with  the  diatoms,  microscopic  vegetable 
organisms  which  separate  silex  from  its  solution  in  the 
water  and  deposit  it  in  thick  beds.     A  large  portion  of 
the  crust  of  the  earth  is,  in  fact,  the  result  of  the  aggre- 
gate labor  of  minute  animals  and  vegetables. 

434.  Disintegration  of  the  Rocks. — In  the  preparation 
of  the  earth  for  the  use  of  man,  the  disintegration  of  the 
rocks  has  been  a  prominent  process.     The  soil  which  he 
cultivates  is,  as  you  have  seen,  a  result  of  this  disintegra- 
tion.    The  mud  that  is  carried  down  the  rivers,  and  de- 
posited in  deltas  or  on  flood-plains,  is  comminuted  rock 
gathered  by  the  waters  from  mountains  and  hills.    The 
ice,  in  glaciers  and  icebergs,  is  continually  grinding  up 
the  rocks  to  add  to  the  soil  of  the  earth.     A  vast  work 
has  been  done  in  the  past  by  water,  in  both  its  liquid 
and  solid  forms,  in  this  preparation  of  the  earth  for  veg- 
etation.   This  was  done  largely,  as  you  have  seen,  in  the 
Glacial  period ;  but  the  work  has  always  been  going  on, 
for  water  has  always  been  in  motion. 

435.  Reconstruction. — In  the  building  up  of  the  earth 
there  has  been  a  vast  amount  of  reconstruction.     The 
rocks  of  which  the  crust  of  the  earth  is  composed  are 
made,  to  a  very  great  extent,  of  materials  derived  from 
the  ruins  of  rocks  previously  made ;  and  often  the  ma- 
terials have  been  used  over  and  over  again.     Disintegra- 


CONCLUDING    OBSERVATIONS.  321 

tion,  then,  has  not  been  of  use  solely  or  chiefly  in  pre- 
paring the  soil  for  vegetation.  Its  principal  use  has 
been  to  procure  the  proper  arrangement  and  condition 
of  the  earth's  crust.  You  have  seen  how  largely,  in 
some  cases,  denudation  has  been  carried  on.  This  is 
chiefly  for  the  purpose  of  removing  the  material  to  local- 
ities where  it  is  required.  It  is  by  this  reconstruction, 
so  extensively  prosecuted,  that  the  proper  diversification 
of  the  surface  of  the  earth  has  been  effected. 

436.  Mechanical,  Chemical,  and  Vital  Agencies. — In  all 
these  disintegrations  and  reconstructions  you  see  a  great 
interplay  of  mechanical,  chemical,  and  vital  forces.     I 
will  cite  here  a  single  example.     Carbonate  of  lime,  in 
the  forms  of  limestone,  chalk,  and  marble,  enters  largely 
into  the  structure  of  the  crust  of  the  earth ;  but  water  is 
continually  dissolving  some  of  this  as  it  finds  it  in  the 
rocks,  and  so  the  ocean  is  kept  supplied  with  it.     This  is 
a  chemical  operation,  the  carbonic  acid  in  the  water  en- 
abling it  to  dissolve  considerable  of  the  carbonate  of 
lime.    Then,  following  it  to  the  ocean,  shell-animals  there 
gather  it  to  make  their  shells,  or  coral  animals  to  make 
their  skeletons.    This  is  a  vital  operation,  for  in  the  bod- 
ies of  these  animals,  by  a  vital  power,  the  carbonate  of 
lime  is  separated  from  the  water  in  which  it  is  dissolved, 
and  is  deposited  in  a  solid  form.    Then,  by  a  mechanical 
operation,  these  shells  and  skeletons  become  massed  into 
solid  rock. 

437.  The  Atmosphere. — One  of  the  most  signal  exam- 
ples of  the  interplay  above  referred  to  is  seen  in  the  re- 
lations which  the  atmosphere  bears  to  the  earth  that  it 
envelops  like  a  robe.    Before  the  Carboniferous  age  it 
was  a  very  different  atmosphere  from  what  it  is  now. 
It  was  then  highly  charged  with  carbonic  acid  gas,  which 
is  carbon,  or  charcoal,  united  with  oxygen.     Now  this 
excess  of  carbon  in  the  air  was  brought  down  in  the 
Carboniferous  age,  and  lodged  in  the  bowels  of  the  earth, 
as  coal,  in  immense  stores,  for  the  future  use  of  man. 

O2 


322  GEOLOGY. 

Observe  how  the  mechanical,  chemical,  and  vital  forces 
were  in  operation  here.  The  carbon  of  the  air  was  made 
a  part  of  the  wood  in  the  enormous  vegetation  of  the 
Carboniferous  era,  through  the  vital  and  chemical  action 
of  the  leaves  (§81,  Part  II.).  Then,  by  chemical  and 
mechanical  operations  together,  this  wood  was  accumu- 
lated under  strata  and  changed  into  coal.  The  same  op- 
erations are  going  on  now,  but  not  to  any  thing  like  the 
extent  that  they  did  in  the  Coal-making  age.  For  ages, 
then,  we  may  say,  the  coal  which  mankind  are  now  burn- 
ing was  stowed  away  in  the  atmosphere,  unseen  in  its 
gaseous  union  with  oxygen,  and  at  the  proper  time  it 
was  brought  down,  and  stowed  in  solid  form  in  the  bow- 
els of  the  earth,  ready  for  man's  use. 

438.  Circulation  of  Matter. — You  see  that  by  the  forces 
which  I  have  mentioned  a  large  portion  of  the  matter  in 
the  world  is  in  constant  motion,  water  being  the  chief, 
but  not  the  only  agent  by  which  the  motion  is  kept  up. 
More  of  it  was  in  circulation  in  former  ages,  when  the 
continents  were  in  process  of  formation,  than  there  is 
now,  when  they  are,  in  a  certain  sense,  completed.    There 
is  enough  of  it  now  remaining  quiet  to  give  "  the  founda- 
tions of  the  earth"  stability,  and  the  great  object  of  the 
present  circulation  of  matter  is  to  keep  up  the  operations 
necessary  to  make  the  earth  a  fit  habitation  for  man. 

439.  Exertion  of  Creative  Power. — It  is  the  notion  of 
some  that  the  Creator  put  a  certain  amount  of  matter 
into  this  ball  that  we  call  earth,  and  then  left  it,  under 
the  operation  of  certain  laws  or  tendencies,  to  work  out 
all  the  results  which  we  see.     In  other  words,  the  ma- 
chinery, mechanical,  chemical,  and  vital,  was  wound  up, 
so  to  speak,,  in  the  beginning,  and  has  not  been  touched 
since  by  the  creative  hand.     That  there  have  been  no 
additions  to  the  matter  in  this  world  since  it  was  first 
launched  into  space  is  probably  true ;  but  that  creative 
power  has  often  been  exercised  in  giving  new  properties 
and  tendencies  to  matter  there  is  the  most  decisive  evi- 


CONCLUDING    OBSEEVATIONS.  323 

dence.  Geology  reveals  the  foot  that  there  was  once  a 
long  age  in  which  there  was  no  life,  vegetable  or  animal, 
upon  the  earth.  After  this  was  passed  life  was  created 
— that  is,  by  creative  power  there  were  given  to  portions 
of  matter  properties  which  matter  of  itself  can  never  orig- 
inate. In  fact,  every  new  species  was  an  independent 
creation.  To  assert,  as  some  have  done,  that  there  never 
was  any  creative  power  exerted,  and  that  all  we  see  is 
the  result  of  the  fortuitous  concourse  of  atoms,  is  a  folly 
wrhich  does  not  merit  a  moment's  notice. 

440.  Development  Theory. — There  is  a  class  of  un- 
founded theories  that  have  been  broached  from  time  to 
time  in  regard  to  the  origin  of  species,  all  of  them  bear- 
ing essentially  the  same  character.  Among  these,  one 
recently  brought  out  by  Darwin,  called  the  development 
theory,  is  just  now  attracting  much  notice.  He  supposes 
that,  at  the  outset,  there  was  "  a  breathing  of  life  into  a 
few  forms,  or  one  form,"  and  that  all  the  living  forms 
which  we  see  were  evolved  from  this  beginning  by  what 
he  calls  "  natural  selection  in  the  struggle  for  existence." 
He  admits,  therefore,  a  divine  creation  of  life  at  the  first, 
but  claims  that  the  development  of  all  living  forms  after 
this  was  directed  by  chance  and  Nature.  All  species,  in 
his  view,  came  from  mere  varieties  that  were  started  in 
this  "  struggle."  In  evolving  thus  one  species  from  an- 
other, it  is  supposed  that  there  were  intermediate  forms, 
and  that  much  time  was  required  for  the  passage  through 
the  gradations.  Unfortunately  for  this  part*  of  the  the- 
ory, geology  steps  in  with  a  most  complete  refutation 
from  its  life-record  in  the  rocks.  Not  a  single  interme- 
diate form  has  been  found  in  all  this  record.  If  they 
had  ever  existed  they  must  have  been  found,  and  that 
abundantly  in  the  midst  of  the  multitude  of  species  that 
appear.  The  changes  demanded  by  this  theory  in  con- 
verting one  species  into  another  are  great  changes.  The 
matter  is  well  stated  by  Page  thus :  "  Given  the  scales, 
fins,  and  gills  of  a  fish — what  the  conditions,  and  what 


324  GEOLOGY. 

the  amount  of  time  necessary  to  transmute  them  into  the 
scutes,  paddles,  and  lungs  of  a  marine  reptile  ?  Given 
the  scutes,  membranous  forearms,  and  stomach  of  a  flying 
reptile — what  the  phases  of  change,  and  what  the  amount 
of  time  required  for  their  transformation  into  the  feath- 
ers, wings,  and  gizzard  of  a  bird  ?  Or,  given  the  four 
hands,  with  partially  opposable  thumbs,  the  low  facial 
angle,  and  the  jabbering,  half-reasoning  of  a  monkey — 
what  the  force  of  conditions,  and  what  the  term  of  time 
for  their  development  into  the  two-handed  dexterity,  the 
erect  aspect,  and  the  eloquent  ratiocinations  of  a  philoso- 
pher of  the  nineteenth  century  ?" 

There  are  many  fundamental  objections  to  this  theory, 
but  this  is  not  the  place  for  a  full  notice  of  them. 

441.  Creation  of  Man. — Such  writers  as  Darwin  and 
Huxley  seem  to  think  of  creation  as  only  a  creation  of 
material  forms,  and  do  not  indulge  in  the  least  the  idea 
of  a  spiritual  creation.  But,  in  truth,  the  grand  event  in 
the  successive  creations  of  which  this  earth  has  been  the 
scene  is  the  creation  of  a  living  SOUL.  Man  is  not  a  mere 
congeries  of  living  organs,  endued  with  certain  proper- 
ties, but  a  spiritual  existence  connected  with  such  a  con- 
geries. Now,  that  this  soul  was  created  as  really  as  the 
congeries  of  organs  with  which  it  is  united  appears  from 
two  facts :  1.  It  has  certain  attributes  which,  as  stated 
in  §  423,  show  that  it  is  to  some  extent  different,  not 
merely  in  degree,  but  in  kind,  from  the  mind  of  brutes, 
and  therefore  had  an  independent  origin.  Not  only  is 
there  no  proof  that  the  mind  of  man  was  generated  from 
the  mind  of  a  monkey,  as  claimed  by  Huxley,  but  there 
is  positive  proof  to  the  contrary  in  this  radical  differ- 
ence. 2.  This  proof  is  enhanced  by  the  fact  that  there 
is  no  difference  in  brain  that  corresponds  at  all  with  this 
mental  difference.  This  utterly  refutes  the  materialistic 
doctrine  that  mind  is  a  mere  product  of  matter,  and  that 
the  differences  of  mind  come  from  differences  in  material 
organization ;  for,  if  this  were  so,  we  should  rightly  ex- 


CONCLUDING    OBSERVATIONS.  325 

i 

pect  (as  I  have  stated  in  my  "Human  Physiology,"  §  523) 
that,  as  the  mind  of  man  is  specifically  different  from  that 
of  the  highest  of  the  inferior  animals,  there  would  be  a 
specific  difference  in  the  brain.  The  fact  that  there  is  no 
such  difference  shows  that  the  mind  of  man  is,  in  a  cer- 
tain sense,  independent  of  material  organization,  and  was 
a  separate  creation,  though  their  connection  establishes 
an  intimate  mutual  dependence  in  man's  present  exist- 
ence in  this  world.  What  folly,  then,  is  the  doctrine  of 
a  "  science,  falsely  so  called,"  which  places  man  only  a 
little  above  the  monkeys,  when  the  Creator  has  declared 
in  his  Word  that  he  "  made  him  a  little  lower  than  the 
angels,"  and  a  true  science  agrees  with  the  declaration  ! 


QUESTIONS. 

[The  numbers  refer  to  the  pages.] 

CHAPTER  I. 

9.  What  is  said  of  the  forms  of  minerals?    In  what  sense  are  all 
minerals  solid  ?     Illustrate  the  relation  which  heat  has  to  the  forms 
of  matter. 

10.  What  are  the  three  kinds  of  substances  that  are  not  mineral? 
State  what  is  said  about  the  lifeless  period  of  the  earth. 

11.  What  is  said  about  the  introduction  of  life  ?     What  of  the  dif- 
ferent results  of  chemical  and  of  vital  action  ?    Explain  what  is  called 
decay.     Give  in  full  the  illustration  in  regard  to  the  egg. 

12.  What  is  said  of  mineral  matter  in  regard  to  organic  substances? 
Of  what  materials  have  many  rocks  been  made  ?     What  is  said  of 
carbonate  of  lime  ?     What  of  the  flinty  rocks  ? 

13.  Give  examples  of  simple  minerals.     What  metals  are  never 
found  uncombined  with  other  elements?     What  metals  are  found 
both  native  and  in  combination  ?     With  what  are  they  combined  ? 
What  is  said  of  oxygen  ?     Of  hydrogen  ?     Of  chlorine  ?     Of  sulphur 
and  carbon  ?     What  is  said  of  the  different  degrees  in  which  miner- 
als are  compound  ?    Mention  the  composition  of  mica  and  of  lapis 
lazuli. 

14.  What  is  said  of  granite  as  a  mixture  of  mineral  compounds  ? 
State  the  relations  of  Mineralogy,  Chemistry,  and  Geology. 

CHAPTER  II. 

14.  What  takes  place  in  crystallization  ?    What  are  familiar  exam- 
ples of  crystals  ?     What  is  the  arrangement  of  the  crystals  of  mica  ? 

15.  What  is  said  of  perfect  and  imperfect  crystallization?     What 
is  an  octahedron  ?     What  is  said  of  the  sizes  of  crystals? 

16.  State  fully  the  difference  between  the  mode  of  crystallization 
and  of  vital  growth.     What  is  said  of  crystals  with  curved  lines  ? 
What  of  spherical  forms  in  some  rocks  ?    What  of  the  arrangements 
of  crystals  ? 

17.  What  is  said  of  the  manner  in  which  mineral  matter  is  depos- 
ited in  living  substances?     What  vegetable  substances  assume  crys- 


328  QUESTIONS. 

talline  forms  ?    Under  what  circumstances  do  they  do  this  ?    What 
is  said  of  forming  crystals  by  deposit  from  solution  ? 

18.  Explain  the  formation  of  frost  and  dew.     Give  examples  of 
the  conversion  of  liquids  and  gases  into  crystals.    What  is  said  of  the 
production  of  crystals  by  the  influence  of  heat  ?    What  of  the  water 
of  crystallization  ?     What  is  an  amorphous  mineral  ?     What  a  di- 
morphous mineral  ? 

19.  What  is  said  of  the  arrangement  of  crystals?     What  of  the 
crystals  of  common  salt?     What  arrangements  are  there  in  rocks 
that  are  somewhat  like  crystallization  ?    What  is  cleavage  ?     What 
are  some  of  its  different  modes  ? 

20.  What  is  said  of  cleavage  in  quartz?    What  are  primary  forms? 
How  many  are  there  ?     Into  how  many  classes  are  they  divided  ? 
What  are  the  crystals  of  the  first  class  ?     What  is  a  rhomb  ?     What 
an  octahedron  ?    What  a  dodecahedron  ? 

21.  Show  how  the  cube  may  be  converted  into  the  octahedron  by 
cleavage.     Show  how  the  octahedron  can  be  converted  into  the  cube. 
What  are  secondary  forms  ?    In  what  two  ways  are  they  produced 
in  nature  ?     Illustrate  the  mode  by  addition. 

22.  What  is  said  of  constancy  in  the  forms  of  crystals?    What  of 
symmetry  ? 

22.  Illustrate  the  analogy  between  the  symmetry  of  the  mineral 
and  that  of  the  living  world. 

CHAPTER  III. 

23.  What  are  the  four  grand  elements  of  which  animal  and  vege- 
table substances  are  composed  ?    What  is  said  of  the  diffusion  of  car- 
bon ?    What  constitutes  the  diamond  ? 

24.  How  can  the  diamond  be  proved  to  be  pure  carbon  ?    How 
does  it  differ  from  charcoal  and  anthracite  ?    What  is  said  of  the  col- 
oring of  diamonds?     What  are  the  qualities  of  diamonds?    What  is 
said  of  their  size  ?    What  are  the  meaning  and  origin  of  the  word 
carat ? 

25.  What  is  said  of  the  cost  of  diamonds  ?  What  of  the  art  of  cut- 
ting them  ?    What  of  the  expense  of  the  process  ?    What  of  the  uses 
of  the  diamond  ? 

26.  What  are  the  chief  localities  in  which  diamonds  are  found  ? 
What  is  said  of  the  modes  of  collecting  them  ?    What  is  the  compo- 
sition of  graphite  ?    What  are  its  properties  ?    What  its  uses  ?    How 
is  it  prepared  for  use  in  pencils  ?    What  is  the  difference  in  com- 
position between  bituminous  and  non-bituminous  coal  ?    What  gas  is 
produced  from  bituminous  coal  ? 

27.  What  is  the  blue  flame  of  imperfectly  burning  anthracite  ?   How 


QUESTIONS.  329 

is  illuminating  gas  obtained  from  bituminous  coal  ?  What  is  coke  ? 
How  is  it  supposed  that  anthracite  coal  was  produced?  How  is  it 
like  coke  ?  How  does  it  differ  from  it  ?  What  is  its  ordinary  com- 
position ?  From  what  does  redness  in  the  ash  come  ?  What  is  said 
of  slag  ?  Why  do  oyster-shells  thrown  into  a  coal  fire  remove  the 
slag  or  clinker  ?  What  is  said  of  certain  uses  to  which  anthracite  is 
sometimes  applied  ? 

28.  What  is  said  of  the  varieties  of  bituminous  coal?    What  of  the 
mineral  called  jet  ?    What  is  lignite  ?     What  proofs  are  there  that 
coal  is  of  vegetable  origin  ? 

29.  How  does  carbon  as  it  is  in  wood  differ  from  carbon  as  it  is  in 
coal  ?     Give  the  comparison  in  relation  to  its  combination  in  wood. 
Give  in  full  what  is  stated  in  regard  to  the  change  in  producing  coal. 
What  is  peat,  and  how  is  it  made  ? 

30.  What  is  said  of  the  depth  and  extent  of  peat  beds  ?     What  of 
the  diffusion  of  coal  in  the  earth  ?     What  is  amber  ?     What  are  its 
properties  ?     What  its  uses  ?     What  is  said  of  specimens  of  it  and 
imitations  of  them  ? 

31.  How  are  the  different  kinds  of  bitumen  produced  ?    What  is 
said  of  asphaltum  ?     What  of  petroleum  ? 

32.  What  of  naphtha  ?     What  is  the  composition  of  carbonic  acid 
gr-s?     What  are  its  qualities?     From  what  sources  is  it  supplied  to 
the  atmosphere?     How  is  its  undue  accumulation  in  the  atmosphere 
prevented  ?     What  is  said  of  localities  where  it  is  produced  in  large 
amount  ?     State  in  full  what  is  said  of  its  agency  in  relation  to  lime- 
stone.   What  is  said  of  the  natural  production  of  illuminating  gas  in 
some  localities  ? 


CHAPTER  IV. 

33.  What  is  said  of  the  crystallization  of  sulphur?    What  of  its  lo- 
calities ?     From  what  ores  is  much  of  our  sulphur  obtained  ?     What 
are  some  of  its  uses  ? 

34.  What  is  the  common  iron  pyrites,  and  why  is  it  so  called? 
What  are  the  forms  of  its  crystals  ?     What  mistake  is  often  made 
about  it?    How  is  it  distinguished  from  gold?    What  use  is  made  of 
it  ?    What  are  the  two  other  kinds  of  iron  pyrites  mentioned  ?    What 
is  said  of  copper  pyrites  ?    What  is  copper  glance?    What  is  said  of 
a  sulphuret  of  a  very  compound  character? 

35.  What  is  galena?     What  is  said  of  it?     In  what  parts  of  the 
United  States  is  it  found  abundantly  ?    What  is  said  of  the  sulphuret 
of  silver  ?    What  of  the  sulphuret  of  antimony  ?    What  of  the  sulphu- 
rets  of  arsenic  ? 

36.  What  of  the  sulphuret  of  mercury  ?    What  of  the  sulphuret  of 


330  QUESTIONS. 

zinc  ?  Give  the  names  and  composition  of  the  three  vitriols.  How 
does  a  sulphate  differ  from  a  sulphuret?  How  are  these  three  sul- 
phates produced  from  the  sulphurets  of  the  same  metals  ?  What  is 
copperas  ?  What  are  its  uses  ?  What  is  said  of  sulphate  of  lead  ? 

37.  What  is  the  composition  of  gypsum  ?    What  are  its  properties? 
What  is  said  of  some  of  its  forms  ?     What  is  anhydrous  gypsum  ? 
What  is  said  of  the  gypsum  found  in  the  Mammoth  Cave  of  Ken- 
tucky ?     State  the  case  related  by  Prof.  Hitchcock,  and  the  mode  of 
detecting  the-  error  indicated. 

38.  What  is  said  of  the  sulphates  of  magnesia  and  soda?     What 
of  the  sulphate  of  baryta  ?    What  of  sulphuric  and  sulphurous  acids  ? 
What  of  sulphureted  hydrogen  ? 

CHAPTER  V. 

39.  What  are  native  metals  ?    To  what  is  the  term  ores  usually  ap- 
plied ?     In  what  different  senses  is  it  used  ?     What  is  said  of  the  po- 
sitions and  associations  of  ores  ? 

40.  Illustrate  the  simplest  method  of  obtaining  metals  from  ores. 
Illustrate  the  other  method  mentioned.     What  is  the  gangue  of  an 
ore  ?    What  is  the  process  termed  washing  ?    Illustrate  the  operation 
of  fluxes.     What  are  the  most  common  ores  of  iron  ?     What  is  said 
of  them  as  colorers  of  rocks  and  soil  ? 

41.  What  is  said  of  meteoric  iron?     What  of  magnetic  iron  ore? 
What  of  hematite  ?     What  of  brown  iron  ore  ? 

42.  What  of  chromic  iron  ?     What  of  carbonate  of  iron  ?     Under 
what  circumstances  is  native  copper  found  ?     What  is  said  of  finding 
silver  with  it  ?    Where  are  famous  copper  mines  ?    What  is  said  of 
the  copper  region  of  Lake  Superior  ? 

43.  How  was  the  copper  produced  in  that  region  ?    What  is  said 
of  the  oxyds  of  copper  ?    How  many  carbonates  of  copper  are  there  ? 
What  is  said  of  the  one  called  malachite  ?     What  of  the  silicate  of 
copper?     What  of  native  lead?     What  is  red  lead?     What  white? 
What  chrome  yellow  ?    What  is  said  of  tin  and  its  ores  ? 

44.  What  is  said  of  zinc  and  its  ores  ?    What  of  antimony  and  its 
compounds  ?     What  of  the  ores  of  cobalt  ?     What  of  nickel  and  its 
ores  ?     What  of  bismuth  and  its  compounds  ? 

45.  What  is  said  of  the  ores  of  manganese  ?     What  are  the  proper- 
ties of  mercury  ?    What  is  related  of  its  discovery  ?    Why  is  it  called 
quicksilver  ?     How  is  its  purity  estimated  by  the  miners  ?    What  are 
its  uses  ? 

46.  In  what  various  conditions  and  combinations  is  silver  found  ? 
In  what  states  is  gold  found  ?     What  is  the  only  compound  that  has 
yet  been  met  with  ?     How  is  gold  distinguished  from  iron  and  copper 


QUESTIONS.  331 

pyrites  ?    In  what  different  forms  is  native  gold  found  ?    What  is 
said  of  some  of  its  localities  ? 

47.  What  is  said  of  the  amount  of  gold  obtained  from  Australia  and 
the  United  States  ?     What  of  the  modes  of  obtaining  gold  ?     What 
of  the  sorting  of  gold  by  natural  operations  ?     Explain  the  operation 
by  which  a  "pocket"  of  gold  is  formed. 

48.  Describe  the  manner  of  effecting  a  large  "washing"  in  the 
search  for  gold.    What  are  the  quantities  of  gold  that  make  it  so  use- 
ful ?     What  is  said  of  gilding  ?     What  of  the  alloys  of  gold  ?     With 
what  is  platinum  generally  found  associated  ?     What  are  its  proper- 
ties? 

49.  What  is  said  of  the  metals  found  in  company  with  platinum  ? 

CHAPTER  VI. 

49.  What  are  oxy-salts  ?    What  are  haloid  salts,  and  why  are  they 
so  called  ? 

50.  What  is  saltpetre  ?    What  is  said  of  its  production  in  nature 
in  different  localities  ?     Of  what  use  is  it  in  the  composition  of  gun- 
powder?    What  is  said  of  the  nitrate  of  soda?     What  is  the  compo- 
sition of  common  salt  ?     What  is  said  of  its  diffusion  in  the  earth  ? 
Under  what  circumstances  is  water  in  seas  or  lakes  exceedingly  salt  ? 
Where  are  there  famous  salt  mines  ?    What  is  said  of  the  mines  of 
Cracow  ?    Where  are  there  hills  of  salt  ?    How  is  salt  obtained  in 
this  country  ? 

51.  What  is  the  composition  of  borax?     What  is  said  of  the  most 
noted  locality  of  it?     Under  what  circumstances  is  boracic  acid 
evolved  ?     What  are  the  different  forms  of  carbonate  of  lime  ?     What 
is  said  of  its  diffusion  in  the  earth  ?     How  is  it  distinguished  from  oth- 
er minerals  that  resemble  it?     What  effect  does  heat  produce  upon 
it?     What  is  hydraulic  lime ? 

52.  What  is  marl?     What  calcareous  tufa?     What  fact  is  stated 
about  chalk  ?     To  what  is  the  name  calcareous  spar  applied  ?    What 
is  said  of  some  of  its  varieties  ? 

53.  What  is  oolitic  marble  ?     Explain  the  formation  of  stalactites 
and  stalagmites.     What  is  said  of  Weyer's  Cave  ?    What  of  the  mag- 
nesian  carbonate  of  lime? 

54.  State  in  full  what  is  said  of  fluor  spar.     What  is  said  of  apa- 
tite ?     What  of  the  salts  of  magnesia  ? 

55.  What  is  said  of  the  chlorid  of  ammonium  ?     What  is  the  com- 
position of  common  alum  ?     What  is  said  of  other  alums?     What  of 
the  feather  alum  ?    What  of  the  phosphates  of  alumina  ? 


332  QUESTIONS. 

CHAPTER  VII. 

66.  What  are  most  of  the  earthy  minerals  ?  What  is  a  silicate  ? 
What  is  said  of  the  compound  character  of  most  earthy  minerals  ? 
What  are  some  of  them  which  are  very  simple  ?  What  proportion 
does  silica  constitute  of  the  earth's  crust  ?  What  is  quartz  ?  What 
is  said  of  silica  in  mica  and  feldspar  ? 

57.  What  are  the  properties  of  silica?     What  is  said  of  its  different 
forms  and  conditions  ?    What  of  its  being  colored  ?    What  is  said  of 
flint  ?     What  of  the  three  varieties  of  quartz  ? 

58.  What  is  said  of  the  crystals  of  quartz  ?    What  of  rock  crystal  ? 
What  of  the  amethyst  ?     What  of  other  crystals  of  quartz  ? 

59.  What  is  chalcedony  ?     What  is  said  of  the  variety  called  car- 
nelian?    What  of  the  agate?    What  of  the  onyx?    What  of  the  cat's 
eye  ?    What  is  the  composition  of  opal  ?     What  is  said  of  its  varie- 
ties ?    What  is  said  of  silica  in  solution  ? 

60.  What  are  the  two  states  in  which  silica  exists?     State  in  full 
what  is  said  of  the  changes  from  the  one  state  into  the  other.    Ex- 
plain petrifaction  with  silica. 

61 .  What  is  said  of  the  silicates  of  magnesia  ?     What  of  the  varie- 
ties of  talc  ?    What  of  serpentine  ?    What  gave  this  name  to  it  ? 
What  is  verd  antique  ?    What  is  said  of  chlorite  ? 

62.  What  is  said  of  pyroxene  ?    What  of  hornblende  ?     What  of 
its  two  remarkable  varieties,  asbestos  and  amianthus?     What  is  the 
composition  of  alumina  ?    What  is  said  of  its  base  ?    What  is  emery  ? 

63.  What  is  sapphire  ?     What  is  said  of  clay  ?    What  of  the  min- 
eral called  spinel  ?    What  of  the  silicates  of  alumina  ?    What  of  feld- 
spar ?     What  are  its  varieties  in  color  and  appearance  ? 

64.  What  is  kaolin  ?    What  is  said  of  albite ?     What  of  labrador- 
ite  ?    What  is  the  composition  of  mica  ?    What  are  its  qualities  ? 
What  its  uses  ? 

65.  What  is  said  of  garnet?    What  of  tourmaline  ?    What  of  the 
composition  of  topaz  ?    What  of  its  use  in  jewelry  ? 

66.  What  is  said  of  the  composition  of  lapis  lazuli  ?    What  are 
beryls  and  emeralds  ?    What  is  said  of  their  size  and  their  value  ? 
What  of  zircon? 

CHAPTER  VIII. 

76.  What  is  the  relation  of  mineralogy  to  geology  ?  What  is  the 
derivation  of  the  word  geology  ?  In  what  senses  does  the  geologist 
use  the  term  rock?  How  many  elementary  substances  are  there? 
Name  those  which  enter  in  any  extent  into  the  composition  of  the 
rocks.  What  is  said  of  the  amount  of  oxygen  in  the  earth's  crust  ? 

68.  What  is  said  of  sulphur  as  a  component  of  rocks  ?    What  of 


QUESTIONS.  333 

hydrogen  ?  State  in  full  what  is  said  of  compounds  existing  in  the 
rocks.  What  examples  are  given  of  incomplete  crystalline  structure 
in  rocks  ? 

69.  What  is  said  of  the  structure  of  sandstone  ?     What  of  rocks 
composed  of  a  single  mineral  ?    What  is  a  pudding-stone  ?    What  a 
breccia  ? 

70.  What  is  said  of  stratified  and  unstratified  rocks?     Give  in  full 
what  is  said  of  silicious,  argillaceous,  and  calcareous  rocks.     How  is 
sulphuric  acid  used  as  a  test  in  examining  rocks  ? 

71.  What  is  the  composition  of  granite?    What  is  syenite?    What 
porphyritic  granite  ?     What  is  said  of  the  colors  of  granite  ?     What 
is  said  of  its  dissemination  in  the  earth  ? 

72.  What  is  said  of  the  uses  of  granite  ?    What  of  the  presence  of 
pyrites  in  it  ?    What  of  the  selection  of  granite  for  building  ?     State 
in  full  what  is  said  of  gneiss. 

73.  What  is  said  of  the  terms  slate,  shale,  and  schist?    What  of 
mica  schist?     Of  hornblende  slate?     Of  talcose  slate  ?    Of  clay  slate? 
What  is  granite  rock?    What  is  said  of  its  varieties?    What  of  its 
uses? 

74.  State  in  full  what  is  said  about  sandstones.     What  is  the  mean- 
ing of  the  word  trap  ? 

75.  What  is  greenstone  ?    What  basalt  ?     What  trachyte  ?    What 
clinkstone  ?     What  is  said  of  the  term  porphyry  ?     What  of  the  term 
amygdaloid?     What  form  do  the  trappean  rocks  tend  to  assume? 
What  examples  are  given  of  this? 

76.  Describe  the  ordinary  structure  of  the  trappean  columns.   What 
is  said  of  the  basaltic  dike  in  North  Carolina  ? 

77.  What  of  Titan's  Piazza?     State  in  full  what  is  said  of  the  trap- 
pean rocks  in  this  country.     What  is  lava  ?     What  are  the  two  classes 
of  lava  ? 

78.  What  is  scoria?     What  is  pumice?    What  its  uses?    What 
are  obsidian  and  pitchstone  ?    What  is  said  of  the  resemblance  of 
lavas  to  the  trappean  rocks  ? 

CHAPTER  IX. 

79.  What  is  said  of  the  substances  of  which  the  earth  is  composed? 
If  the  surface  of  the  earth  were  not  diversified,  what  would  be  the  ar- 
rangement of  the  water  and  the  air?     Give  in  full  what  is  said  of 
the  weight  of  the  earth.     What  estimates  are  given  of  the  increase  of 
condensation  toward  the  centre? 

80.  Explain  what  is  represented  by  Fig.  31. 

81.  Show  how  much  this  figure  exaggerates  the  amount  of  equato- 
rial bulging.     What  influence  has  this  bulging  upon  the  earth's  rev- 


334  QUESTIONS. 

olution  ?     What  is  meant  by  the  crust  of  the  earth  ?     In  what  ways 
has  knowledge  of  it  to  great  depths  been  obtained  ? 

82.  What  is  said  of  the  foundation  of  this  crust?     What  of  its 
thickness?     What  is  the  proportion  of  land  and  water  on  its  surface? 
What  is  said  of  the  elevations  on  the  earth's  crust?     What  of  the  de- 
pressions ?     What  of  the  shallows  of  the  ocean  ?     What  of  bodies  of 
water  between  certain  portions  of  land  ? 

83.  What  comparison  is  made  between  the  equatorial  bulging  and 
the  mountainous  elevations  ?    What  between  the  elevations  and  de- 
pressions ?     What  is  said  of  the  ocean  near  Newfoundland  ?     What 
of  the  general  arrangement  of  the  land?    What  of  its  divisions? 
What  of  the  position  of  the  Atlantic  and  Pacific  Oceans  ? 

84.  What  is  said  of  a  certain  arrangement  of  the  waters  noticed  by 
Guyot  ?     What  of  the  arrangement  of  the  mountains  ? 

85.  What  is  said  of  their  relation  to  the  oceans  ?     What  of  varia- 
tions in  the  arrangements  of  chains  of  mountains  ?    What  as  to  their 
prevailing  directions  ?     State  in  full  what  is  said  of  volcanoes.    What 
is  a  plateau  ? 

86.  What  are  called  lowlands  ?     Give  examples  of  extensive  low- 
lands.    What  relations  have  mountains  to  plateaus  and  lowlands? 
What  are  table-lands  ?     Give  examples  of  extensive  plateaus.     How 
do  these  compare  in  arrangement  with  what  we  often  see  on  a  small 
scale  ? 

87.  State  in  full  what  is  said  of  rivers.     What  is  said  of  lakes? 
How  do  mountains  affect  the  fertility  of  regions?     How  are  winds 
produced  ?     Give  what  is  said  of  the  prevalent  winds. 

88.  State  in  full  what  is  said  of  the  influence  of  mountains  on  the 
fall  of  rain,  and  the  consequent  difference  between  America  and  Eu- 
rope.    What  would  have  been  the  condition  of  North  America  if  the 
Rocky  Mountains  were  on  its  eastern  side  and  the  Appalachians  on 
the  western  ?     What  is  said  of  the  circulation  of  water  ? 

89.  What  is  said  of  systematic  currents?     What  comparison  is 
made  in  regard  to  the  circulation  of  water  ?     What  is  said  of  the  di- 
versification of  the  earth's  surface  ?     What  of  the  treasures  in  the 
earth's  crust  ? 

CHAPTER  X. 

90.  What  is  said  of  the  apparent  discrepancy  between  the  Scripture 
account  of  the  creation  and  the  ideas  of  geologists  ?     In  what  sense  is 
the  word  present  used  in  the  title  of  this  chapter  ?     What  are  the 
agents  of  change  in  the  earth  ? 

91.  State  in  full  what  is  said  of  the  aqueous  and  igneous  agencies. 
Illustrate  the  influence  of  different  degrees  of  rapidity  in  the  flow  of 
water  on  the  removal  of  materials. 


QUESTIONS.  335 

92.  State  in  full  what  is  said  of  deposits  in  rivers  and  on  their  bor- 
ders. 

93.  Explain  the  mode  of  improving  rivers  illustrated  by  Fig.  35. 

94.  What  is  said  of  deposits  in  lakes  ?     State  the  facts  in  regard  to 
the  Lake  of  Geneva.     What  is  said  of  the  lakes  of  our  country? 

95.  What  is  a  delta,  and  why  is  it  so  named  ?     Describe  the  mode 
of  its  formation.     What  is  said  of  bars  and  islands  formed  in  connec- 
tion with  deltas  ? 

96.  Why  is  there  no  delta  at  the  mouth  of  the  Amazon  ?     Give  in 
full  what  is  said  of  the  sediment  deposited  from  the  Ganges  in  the 
Bay  of  Bengal.     What  is  said  of  Louisiana,  and  of  the  amount  of 
matter  brought  down  by  the  Mississippi  ? 

97.  What  is  said  of  the  extent  of  deltas?     What  of  the  consolida- 
tion of  sediment  from  rivers  into  rock  ?     Give  examples  of  the  en- 
croachment of  water  upon  land. 

98.  What  is  said  of  the  mechanical  action  of  water  upon  rock? 
What  is  said  of  "  Pulpit  Rock  ?" 

99.  Illustrate  the  erosive  work  which  water  does  by  rubbing  one 
solid  against  another.     What  is  said  of  pot-holes?     Give  the  state- 
ment in  regard  to  Niagara  Falls. 

100.  What  is  said  of  the  canons  of  Colorado  ?    What  of  the  erosion 
by  the  River  Simeto  ?     State  in  full  what  is  said  of  the  constancy  of 
the  action  of  water  in  erosions. 

102.  How  does  frost  disintegrate  rocks  ?    How  do  the  results  differ 
in  hard  and  soft  rocks?     What  is  a  talus,  and  how  is  it  formed? 
What  is  said  of  the  sorting  of  fragments  in  a  talus  ?     State  in  full 
what  is  said  of  the  chemical  action  of  water  on  rocks. 

103.  Explain  weathering.     What  is  said  of  the  Druidical  monu- 
ments ?     What  of  the  weathering  of  hard  and  of  soft  rocks?     What 
of  weathering  in  the  soil  ? 

104.  Give  the  statement  about  the  boulder.    What  is  said  of  the 
Loggan  stones  ?     How  do  the  present  effects  of  glaciers  and  icebergs 
compare  with  their  effects  in  past  ages  ?    Why  is  a  glacier  said  to  be 
a  river  of  ice? 

105.  Of  what  is  a  glacier  made?     What  are  lateral  and  medial 
moraines  ?     Give  in  full  what  is  said  about  the  termination  of  a  gla- 
cier. 

107.  What  is  said  of  the  markings  and  other  effects  of  glaciers  ? 

108.  Describe  the  formation  of  terminal  moraines.     How  are  ice- 
bergs produced  ?     What  is  said  of  their  height  ?     What  proportion 
of  an  iceberg  is  above  the  surface  of  the  water  ? 

109.  How  extensive  are  some  icebergs?     What  is  stated  of  their 
numbers  ?    What  is  said  of  their  dropping  fragments  of  rock  ?    What 
of  their  dragging  and  stranding? 


336  QUESTIONS. 

110.  State  in  full  what  is  said  of  the  leveling  operations  of  water. 
What  is  said  of  the  agency  of  heat  ? 

111.  Of  what  benefit  to  the  earth  are  volcanoes  ?    What  is  the  dis- 
tinction between  extinct  and  active  volcanoes  ?     How  is  it  supposed 
that  an  eruption  is  produced  ?     Describe  the  phenomena  of  an  erup- 
tion. 

112.  When  was  the  first  eruption  of  Vesuvius  that  is  on  record? 
What  was  its  condition  just  before  this  ?     State  in  full  what  is  said 
of  the  burial  of  Herculaneum  and  Pompeii.     What  happened  to  Ve- 
suvius in  1822  ?    What  is  the  size  of  Etna  ?    What  is  said  of  its  erup- 
tion in  1669  ? 

113.  What  does  Mantell  say  of  one  of  Etna's  eruptions? 

114.  Describe  the  crater  of  Kilauea.     Where  is  Tomboro?    Give 
Lyell's  description  of  the  effects  of  one  of  its  eruptions. 

115.  Give  the  facts  in  regard  to  Graham's  Island.     What  is  said 
of  other  volcanic  islands  ? 

116.  Give  the  statement  about  an  island  near  Iceland. 

117.  How  may  changes  in  the  temperature  of  the  earth's  crust 
cause  earthquakes  ?     Give  Prof.  Dana's  illustration.    What  is  said  of 
the  two  vibrations  produced  by  an  earthquake  ?     State  the  effects  of 
earthquakes. 

118.  What  is  said  of  solfataras ?    What  of  hot  springs?    Describe 
the  geysers  of  Iceland. 

119.  Explain  their  operation. 

120.  State  in  full  what  is  said  of  sand  being  moved  by  wind. 

121.  What  is  said  of  gradual  alterations  of  levels  ?     Give  the  state- 
ment about  the  Temple  of  Jupiter  Serapis. 

122.  What  does  Hugh  Miller  say  about  the  old  coast-lines  of  Scot- 
land ?     State  the  evidences  of  a  gradual  change  of  level  in  Sweden 
and  Norway. 

1 23.  What  is  said  of  organic  agencies  ?    What  of  changes  made  by 
man? 

CHAPTER  XI. 

123.  What  is  said  of  the  succession  of  changes  in  the  construction 
of  the  earth's  crust  ? 

124.  What  is  said  of  the  development  of  life  upon  the  earth  ?    Why 
will  what  you  have  learned  of  present  changes  help  you  to  understand 
changes  in  the  past?     How  does  the  geologist  arrive  at  his  conclu- 
sions?    By  what  comparisons  as  to  composition  does  he  determine 
the  origin  of  rocks  ? 

125.  State  the  case  of  the  shells  found  in  rock.     State  the  observa- 
tion made  about  different  rocks  that  contain  shells.     State  the  rea- 
soning about  the  pudding-stone. 


QUESTIONS.  337 

126.  What  observations  are  made  by  the  geologist  in  regard  to 
tracks,  ripples,  etc.  ?     State  the  case  of  the  slab  found  in  Pottsville. 
What  are  the  two  grand  classes  of  rocks  ?     What  is  the  construction 
of  stratified  rocks  ?    Why  are  they  called  aqueous  rocks  ?     Why  fos- 
siliferous  rocks  ? 

127.  What  are  metamorphic  rocks  ?    What  is  the  derivation  of  the 
name  ?    What  proof  is  mentioned  that  heat  is  the  chief  agent  of  met- 
amorphism  ?     What  is  said  of  the  appearance  and  the  formation  of 
unstratified  rocks  ? 

128.  What  is  the  usual  difference  in  position  of  the  stratified  and 
the  unstratified  rocks  ?    What  is  said  of  trappean  rocks  ?    What  is  a 
stratum  ?    What  a  stratification  ?    What  are  laminae  ?    What  is  said 
of  them  as  seen  in  shales  and  micaceous  sandstones? 

129.  What  is  said  of  the  deposition  of  laminae  ?    How  is  the  term 
formation  used?    What  are  joints  and  master-joints? 

130.  What  is  said  of  the  regularity  of  these  divisions  in  the  rocks? 
What  is  stated  about  the  cliffs  of  Cayuga  Lake?    What  is  cleavage 
in  rocks  ? 

131.  What  is  said  of  the  order  of  succession  in  the  strata?     Give 
the  comparison  of  Phillips.     What  remarkable  fact  is  stated  about 
the  chalk  formation  ?     What  is  said  of  flexures  of  strata?    What  of 
the  circumstances  under  which  they  were  produced  ?     State  the 
comparison  in  regard  to  ice. 

132.  Illustrate  the  mode  of  producing  the  flexures.     What  fact 
bearing  on  this  is  related  by  Lyell  ? 

133.  What  is  said  of  upheavals  of  strata  accompanied  by  fracture? 
What  of  chasms,  caverns,  and  natural  bridges  ?     Illustrate  the  man- 
ner in  which  strata  are  brought  to  view  by  upheavals. 

134.  What  is  true  of  strata  found  in  a  vertical  position?     Show 
how  strata  may  be  supposed  to  be  horizontal  when  they  are  far  from  it. 

135.  Explain  dip  and  strike.     Show  what  anticlinal  and  synclinal 
lines  are. 

136.  Show  in  detail  how  strata  may  be  laid  down  on  a  map  when 
they  outcrop. 

137.  Show  how  the  thickness  of  the  strata  in  the  above  case  may 
be  ascertained. 

138.  What  is  said  of  the  extent  of  knowledge  that  can  be  acquired 
by  such  observations  as  have  been  detailed  ? 

139.  Show  what  are  conformable  and  unconformable  strata.    What 
are  faults  ? 

140.  What  is  denudation  ?     What  is  said  of  the  extent  of  the  re- 
sults effected  by  it  ?     State  the  case  illustrating  denudation  occurring 
with  a  fault. 

141 .  State  the  case  of  the  great  fault  spoken  of  by  Mr.  Lesley. 

F 


338  QUESTIONS. 

142.  Point  out  the  different  modes  in  which  mountains  have  been 
made. 

143.  Mention  the  three  ways  in  which  valleys  have  been   made. 
Of  what  materials  are  volcanoes  constructed  ?    Give  the  facts  in  re- 
gard to  Fusiyama. 

145.  Indicate  the  mode  of  formation  of  volcanic  cones.     How  are 
irregularities  in  their  form  caused  ?     What  is  said  of  the  formation 
of  trappean  rocks  ? 

146.  How  is  a  sunk  dike  formed  ?    How  a  raised  dike  ?   What  com- 
parison is  made  by  Hugh  Miller  in  speaking  of  the  trap  dikes  about 
Edinburg  ?     What  is  said  of  East  and  West  Kocks  in  New  Haven  ? 
What  does  Hugh  Miller  say  about  trap  scenery  ?    How  were  the  trap 
rocks  formed? 

147.  What  is  said  of  the  commotion  attending  their  formation  ? 
What  is  the  statement  of  Hugh  Miller  and v the  criticism  upon  it? 
What  is  said  of  the  pillar-like  form  often  assumed  by  the  trap  rocks  ? 
What  are  veins?     What  is  said  of  veins  in  granite? 

148.  State  what  is  said  of  the  granite  boulder  of  which  a  section  is 
given.     How  do  veins  differ  from  dikes  ? 

149.  What  is  the  vein-stone  or  gangue  ?    What  is  said  of  the  man- 
ner in  which  dikes  and  veins  are  formed  ?     What  is  a  lode  ?     What 
is  drift  ?     In  what  parts  of  the  continents  does  it  appear  ?     By  what 
means  was  it  transported  to  its  localities  ?    How  can  it  be  ascertained 
where  it  came  from  in  any  case? 

150.  What  traces  of  the  passage  of  drift  are  found?     What  is  said 
of  alternate  elevations  and  subsidences  of  the  earth's  crust?    What 
prolonged  subsidence  is  spoken  of  by  Lyell  ?    What  is  said  of  the  sub- 
sidences and  elevations  of  the  Coal  age  ? 

151.  By  what  means  are  pebbles,  sand,  and  earth  produced  from 
rocks  ?    What  is  soil  ?    What  may  be  said  of  the  additions  to  it  from 
decay  ?     Is  the  preparation  of  soil  by  disintegration  of  rock  to  be  re- 
garded only  as  a  destructive  process  ?     How  may  earth-worms  and 
ants  be  considered  as  geological  workers  ? 

152.  Describe  the  work  of  the  earth-worms.     Describe  that  of  the 
ants. 

154.  Indicate  the  manner  in  which  coral  reefs  are  built.     To  what 
climates  are  coral  animals  confined  ?     Why  are  there  none  on  the 
western  coast  of  South  America?    What  is  the  extent  of  the  reef  on 
the  coast  of  New  Holland  ?     Explain  the  difference  between  fringing 
and  barrier  reefs.     How  was  Florida  made  ? 

155.  What  are  atolls  and  lagoons  ?     Show  how  an  atoll  is  formed 
by  means  of  Figs.  81  and  82. 

156.  What  is  said  of  the  number  of  coral  islands  in  the  Pacific 
Ocean  ?    What  of  the  depth  to  which  they  reach  in  the  water  ?    What 


QUESTIONS.  339 

of  the  time  occupied  in  their  formation  ?    What  is-  said  of  the  forma- 
tion of  limestone  rocks  from  shells  ? 

157.  What  is  said  of  the  foraminifera  ?     What  of  the  agency  of 
minute  animals,  in  comparison  with  large  ones,  in  forming  the  earth's 
crust  ?     What  is  stated  about  the  nummulites  ?     What  is  oaze,  and 
what  is  said  of  it  ? 

158.  Of  what  are  the  limestone  strata  quarried  near  Paris  com- 
posed?   What  did  Ehrenberg  find  in  chalk?     Mention  the  observa- 
tions of  Soldani.     What  is  said  of  silicious  shells  ?     What  of  the 
white  clay  about  Richmond  ? 

159.  What  of  the  tripoli  of  Germany?    What  is  supposed  to  be  the 
origin  of  the  flint-stones  found  in  chalk  ?    What  is  said  of  the  extent 
of  the  agency  of  silicious  animalcules  and  plants  in  forming  rocks  ? 
What  is  the  nature  of  diatoms  ?     What  is  said  of  the  formation  of 
seas,  lakes,  and  rivers  ?    What  is  said  of  plan  in  the  construction  of 
the  earth  ? 

160.  What  is  said  of  life  in  the  different  ages  of  the  earth  ?    What 
of  making  out  the  order  of  succession  in  the  rocks  by  the  life-record  ? 

161.  What  is  said  of  the  resemblances  of  present  living  forms  to 
those  of  the  past  ?     What  is  the  nature  of  the  evidence  from  the  life- 
record  as  to  the  relative  ages  of  the  strata  ?    What  is  said  of  the  cor- 
respondence of  the  evidence  in  different  countries  ?    Illustrate  this 
by  reference  to  the  coal  formation. 

162.  What  are  fossils  ?    What  is  the  origin  of  the  term  ?    In  what 
different  degrees  are  fossils  preserved  ?    What  is  said  of  petrified  fos- 
sils?    What  of  casts  of  living  substances  made  by  some  mineral? 
Why  may  coal,  strictly  speaking,  be  considered  a  fossil  ?     State  what 
is  said  of  the  preservability  of  different  fossils. 

163.  Give  in  full  what  is  said  of  the  abundance  of  fossils.    Explain 
the  principles  on  which  Cuvier  and  others  have  investigated  fossils. 

164.  Show  how  these  principles  are  applied  by  most  people  to  a 
limited  extent.    How  is  skill  acquired  in  applying  them  ?     What  is 
said  of  their  application  to  vegetables  ?    What  is  the  derivation  of  the 
word  Palaeontology?    What  is  said  of  the  general  plan  of  living 
structures  ? 

165.  What  are  the  Acrogens,  and  why  are  they  so  named?    What 
are  the  Gymnogens,  and  what  is  the  derivation  of  their  name  ?    What 
purpose  have  these  and  the  Acrogens  served? 

167.  What  relations  had  the  Acrogens  and  Gymnogens  to  animal 
life? 

169.  What  are  the  Endogens  ?    What  is  their  chief  purpose  ? 

170.  What  is  meant  by  a  geological,  and  what  by  a  zoological 
agency  ?     Explain  the  meaning  of  the  term  Endogens.     How  does 
the  mode  of  growth  in  an  Exogen  differ  from  that  of  an  Endogen  ? 


340  QUESTIONS. 

What  is  the  difference  in  their  stems  ?  What  is  the  use  of  the  Exo- 
gens  ?  What  is  said  of  the  presence  of  the  Endogens  and  Exogens  in 
the  life-record  ?  What  difficulty  is  there  in  the  study  of  fossil  botany? 
What  error  is  mentioned  as  having  risen  from  the  scantiness  of  the 
evidence  ?  What  is  said  of  the  veins  in  the  leaves  as  furnishing  a 
ground  of  distinction  in  the  classification  of  vegetable  remains  ? 

173.  Why  is  the  study  of  fossil  zoology  more  satisfactory  than,  that 
of  fossil  botany  ?     Give  in  full  what  is  stated  about  Protozoans. 

174.  What  are  the  classes  of  Radiates  ?    Why  are  they  so  called  ? 
State  what  is  said  of  them. 

176.  Why  are  Mollusks  so  called?     What  does  this  division  in- 
clude ?     How  far  are  Mollusks  zoological  in  their  relations  ?     Why 
are  they  of  great  value  in  geological  investigations  ?     Why  are  the 
Articulata  so  named  ?     What  does  this  4ivision  include  ?     What  is 
said  of  the  relations  of  the  Articulata  ?    What  of  the  variety  of  their 
character  ? 

177.  What  are  the  characteristics  of  the  Vertebrata  ? 

178.  What  is  said  of  the  spinal  marrow  of  the  Vertebrates  ?    What 
are  the  four  grand  divisions  of  this  portion  of  the.  animal  kingdom  ? 
What  is  said  of  the  intellectual  qualities  of  the  Vertebrata  ?     What 
of  their  relations,  geological  and  zoological  ?    What  of  their  relations 
to  the  higher  orders  of  the  vegetable  world  ? 

179.  What  is  said  of  the  mode  of  division  of  the  earth's  history  ? 
What  is  Dana's  division  ? 

180.  Give  the  division  of  time  into  five  periods,  explaining  their 
names.     How  definite  are  the  boundaries  of  the  ages  ?    What  is  said 
of  foreshadowing  ? 

181.  What  examples  of  foreshadowing  are  cited  ?    What  is  said  of 
the  idea  on  which  the  ages  are  named? 

CHAPTER  XIII. 

181.  What  is  said  of  the  fused  state  of  the  earth? 

182.  What  of  the  time  occupied  in  cooling  the  earth  sufficiently  to 
form  a  crust  ?    What  of  the  length  of  time  before  life  appeared  on  the 
earth?     State  in  full  what  is  said  of  the  floor  of  the  earth's  crust. 
What  were  the  changes  that  attended  the  beginning  solidification  of 
the  earth's  crust? 

183.  What  agency  had  denudation  in  this  beginning  of  the  forma- 
tion of  land  ?     Give  Dana's  statement  in  regard  to  the  land  formed 
in  the  Azoic  age.    What  is  said  of  the  extent  of  the  lands  that  then 
appeared  above  the  surface  of  the  waters  ? 

184.  What  was  the  shape  of  North  America  in  the  Azoic  age? 
What  does  Agassiz  say  of  this  island  ?     How  was  Europe,  in  contrast 
with  North  America,  in  this  age  ? 


QUESTIONS.  341 

185.  What  is  said  of  the  thickness  of  the  Azoic  strata  ?    What  of 
the  upheavals  and  flexures  of  them  ?    What  of  the  rocks  of  this  age  ? 
What  of  the  temperature  of  the  forming  crust? 

186.  Give  Hugh  Miller's  description  of  the  commotions  attending 
its  formation. 

187.  Why  could  not  life  exist  in  this  age  ?   What  was  the  condition 
of  the  surface  of  the  land  at  the  end  of  it  ? 


CHAPTER  XIV. 

*-  187.  Why  is  it  inferred  that  life  was  introduced  at  the  beginning 
of  the  Silurian  age  ? 

188.  Why  is  it  supposed  by  some  that  life  was  introduced  before 
this  ?    What  reason  have  we  for  saying  that  life  was  created  ?    What 
is  said  of  species  ?    What  are  the  rocks  of  this  age  ?    What  is  said  of 
the  rocks  at  Niagara  Falls  ? 

189.  Why  is  this  called  the  Silurian  age?    What  is  the  arrange- 
ment of  the  Silurian  system  in  New  York  ? 

190.  What  is  the  geographical  distribution  of  the  Silurian  rocks,  so 
far  as  ascertained?    State  the  origin  of  the  copper  of  Lake  Superior. 
What  is  said  of  the  salt  springs  in  this  country  ? 

191.  State  Dana's  way  of  accounting  for  the  great  accumulation 
of  salt  in  the  State  of  New- York.     Trace  the  comparison  in  regard 
to  the  lagoon.     How  is  the  salt  obtained  from  the  springs  in  New 
York? 

192.  How  was  the  gypsum,  which  abounds  in  the  Silurian  forma- 
tion in  New  York,  produced  ?   Where  gypsum  and  salt  are  found  to- 
gether, how  are  they  separated?     State  in  full  what  is  said  of  "the 
Silurian  beach." 

193.  What  is  said  of  the  traces  left  by  water  ?    State  in  full  what 
is  said  of  life  in  the  Silurian  age. 

194.  What  was  the  condition  of  the  atmosphere  in  this  age  ?    Show- 
how  the  animal  world  was  adapted  to  it.     Give  what  Agassiz  says  of 
this  adaptation.     What  was  the  source  of  the  carbonaceous  matter  in 
the  Silurian  shales? 

195.  What  are  the  Hydrozoa  and  Bryozoa  of  this  age?    What  is 
said  of  the  corals  and  echinoderms? 

196.  What  of  the  chain  coral  ?    What  of  the  crinoids  ? 

197.  Name  the  three  classes  of  Mollusks,  and  state  what  is  said  of 
each. 

198.  What  are  the  Brachiopods,  and  what  is  said  of  them  ?    What 
is  said  of  the  Lingula?     Of  the  Orthoceras?     What  of  the  Cephalo- 
pods  in  this  age,  in  contrast  with  the  present  ? 

199.  What  is  said  of  the  Trilobites? 


342  QUESTIONS. 

200.  What  evidence  is  there  that  the  climate  of  this  age  was  quite 
warm  over  most  of  the  earth  ?  What  evidence  is  there  that  the  sun 
shone  clearly  then  ? 


CHAPTER  XV. 

201.  What  were  the  rocks  formed  in  the  Devonian  age?     Indicate 
the  extent  of  the  Devonian  system  in  this  country. 

202.  What  is  its  extent  in  Europe  ?     Detail  the  interesting  exam- 
ple of  geological  investigation  mentioned.     How  prominent  were  the 
coral  formations  in  this  age  ?    Mention  the  remarkable  display  of  De 
vonian  corals  in  Kentucky. 

203.  What  two  elegant  corals  are  mentioned  as  being  found  in  that 
locality  ?    What  different  kinds  of  rock-making  were  going  on  at  the 
same  time  in  the  Devonian  age  ?     What  is  said  of  Devonian  vegeta- 
tion? 

204.  What  of  Devonian  animals  ?    What  of  Mollusks  ?    What  of 
Trilobites  ? 

205.  What  of  Crustaceans  ? 

206.  What  is  the  discovery  of  Agassiz  in  regard  to  the  classifica- 
tion of  fishes?     Of  what  value  is  this  to  geology?     Name  the  four 
orders  of  Agassiz,  and  state  what  is  said  of  each. 

207.  What  is  said  of  the  comparative  prevalence  of  these  orders  in 
different  ages  ?     Describe  the  Coccosteus. 

208.  Describe  the  Pterichthys.    What  is  said  of  the  appearance  of 
its  remains  in  the  rock  ?     Why  is  the  Cephalaspis  so  named  ? 

209.  Describe  the  Asterolepis. 

210.  What  are  comprehensive  types  ?    What  is  said  of  their  compar- 
ative prevalence  in  different  ages  ?   What  is  said  of  the  tails  of  ancient 
fishes  ?   What  of  the  abundance  of  fishes  in  the  Devonian  age? 

211.  What  of  the  state  in  which  their  remains  are  often  found? 
What  was  the  condition  of  the  North  American  continent  at  the  end 
of  the  Azoic  age  ?     What  at  the  end  of  the  Silurian  ?    What  addi- 
tions were  made  to  it  in  the  Devonian  ?    What  results  did  upheavals 
in  the  west  and  the  east  produce  at  the  close  of  this  age  ?     What  re- 
sults where  the  city  of  Cincinnati  now  stands  ? 

212.  What  does  Agassiz  say  of  the  abundance  and  richness  of  Silu- 
rian remains  found  in  that  locality  ?     What  is  said  of  the  scenery  of 
the  Devonian  age  ? 


CHAPTER  XVI. 

213.  How  does  the  name  of  the  age  of  coal  differ  from  the  names 
of  the  other  ages?    What  peculiar  propriety  is  there  in  the  name ? 


QUESTIONS.  343 

214.  What  is  the  estimated  amount  of  coal  in  all  the  coal-fields  of 
North  America?    What  of  all  in  Great  Britain  ?     In  Belgium  ?    In 
France  ?     What  facts  are  stated  about  the  introduction  of  anthracite 
into  full  use  in  this  country  ?     What  estimate  is  made  of  the  length 
of  time  the  coal  of  this  country  will  last?     What  statements  are 
made  about  the  extent  of  coal-fields  ? 

215.  Describe  the  arrangement  of  the  carboniferous  strata.    What 
are  called  the  coal-measures  ?     In  what  way  do  the  rocky  strata  in 
these  measures  differ  from  other  rocks  ?     Of  what  practical  value  is 
the  knowledge  of  this  difference  ?     What  does  Hitchcock  say  on  this 
point  ?    What  is  the  under-day,  and  what  is  said  of  it  ?    What  is  the 
proportion  of  coal  to  rock  in  the  coal-measures  ? 

216.  What  is  the  sub-carboniferous  period?   What  is  the  thickness 
of  the  floor  of  the  coal-measures  laid  in  this  period  ?     Of  what  was 
it  made  ?    What  is  the  relative  position  of  the  sub-carboniferous  and 
carboniferous  strata  ?     What  similarity  of  arrangement  was  there  in 
the  Silurian  and  Devonian  ages  and  the  sub-carboniferous  period? 

217.  In  what  two  respects  did  this  arrangement  differ  in  the  sub- 
carboniferous  period  from  that  of  the  Silurian  and  Devonian  ages  ? 
What  is  the  difference  between  the  burning  of  wood  and  the  making 
of  charcoal  ?     Explain  the  chemistry  of  the  formation  of  coal.    Why 
is  this  process  called  eremacausis  ?    What  is  said  of  the  decay  of  veg- 
etable matter  ? 

218.  What  is  said  of  the  agency  of  pressure  in  making  coal  ?  What 
is  the  difference  between  bituminous  and  non-bituminous  coal  ?    What 
is  the  flame  of  bituminous  coal  ?     What  that  of  imperfectly  burning 
anthracite  ?     How  is  it  supposed  that  anthracite  was  produced  from 
bituminous  coal  ?     How  does  it  differ  from  coke  ?     What  is  said  of 
the  vegetable  growth  from  which  coal  was  formed  ? 

219.  What  is  said  of  the  accumulation  of  material  for  a  coal-bed? 
Describe  what  took  place  after  all  the  material  was  deposited.    What 
is  stated  about  the  number  of  coal-beds  ?     What  does  Hugh  Miller 
say  of  the  alternate  subsidences  and  elevations  of  this  age  ? 

220.  What  is  said  of  the  impurities  of  coal?     What  of  the  calcula- 
tions as  to  the  time  required  for  the  formation  of  the  coal-measures  ? 
What  of  the  plants  whose  remains  are  found  in  them  ? 

221.  What  is  said  of  the  remains  of  leaves  found  in  the  rocks? 
State  the  experiments  of  Professor  Goppert. 

222.  What  is  said  of  the  Calamites  ?    What  of  Sigillaria  and  Stig- 
maria  ? 

223.  What  of  the  Lepidodendron  ?     What  of  the  Ferns  ? 

224.  What  of  the  Conifers  ? 

225.  What  is  the  general  view  given  of  carboniferous  vegetation  ? 

226.  What  does  Page  say  of  the  beauty  of  this  vegetation  ?     What 


344  QUESTIONS, 

is  said  of  leaf-scars  ?    What  was  the  peculiar  condition  of  the  atmos- 
phere up  to  the  Carboniferous  age  ? 

227.  What  change  was  made  in  it  during  that  age  ?     How  was  it 
done?     State  the  comparison  made  in  regard  to  this  transfer  from 
the  gaseous  to  the  solid  state.     What  is  said  of  the  climate  of  this 
age  ?    What  was  the  character  of  Carboniferous  scenery? 

228.  What  is  said  of  the  extent  of  the  successive  platforms  of  vege- 
tation ?     What  change  occurred  in  the  scene  when  the  accumulated 
material  was  submerged  for  conversion  into  coal  ?     What  is  said  of 
the  animals  of  this  age  ? 

229.  What  is  said  of  the  coral  animals  ?     What  of  the  crinoids , 
and  sea-urchins  ? 

231.  What  of  the  Crustaceans?     What  of  the  Reptiles?     State 
the  facts  about  the  Pottsville  reptile.     What  is  said  of  the  fishes  ? 

232.  State  in  full  what  is  said  of  the  Lepidosteus  and  of  the  gar- 
pike  of  the  present  age.     What  is  said  of  the  Mollusks  ?     What  of 
the  Productus  spinulosus  ? 

233.  What  of  the  Spirifer  ?     From  what  does  the  Permian  period 
get  its  name  ?     What  is  said  of  the  Permian  strata  in  this  country  ? 
What  of  them  in  Europe  ? 

234.  What  are  the  Permian  rocks  in  this  country?     What  is  said 
of  the  Permian  limestones  of  Europe?     What  was  the  condition  of 
North  America  at  the  end  of  the  age  of  Coal  ?    What  is  said  of  the 
disturbances  of  the  coal-measures  ? 

235.  What  is  said  of  the  connection  of  metamorphosis  with  these 
disturbances  ?     What  of  their  being  systematic  ?     What  of  their  rate 
of  movement  ?   What  of  certain  valuable  results  of  metamorphosis  at 
this  time  ?     What  of  the  debituminization  of  coal  ?     What  of  denuda- 
tion ?    What  of  the  differences  of  the  forms  of  life  in  different  ages  ? 

236.  When  did  vertebrates  first  appear  ?     When  reptiles  ?     What 
class  of  animals  did  not  appear  till  after  Palaeozoic  time  ?     What  is 
said  of  the  disappearance  of  animals  ?     What  of  the  destruction  of 
life  at  the  close  of  the  Carboniferous  age  ? 

CHAPTER  XVII. 

236.  What  are  the  divisions  of  the  age   of  Reptiles?    Whence 
conies  the  term  Triassic  ?     Whence  Jurassic  ? 

237.  What  is  said  of  the  term  Oolitic  ?     What  of  the  term  Creta- 
ceous ?    What  is  stated  about  the  Cretaceous  system  in  this  country  ? 
State  in  full  what  is  said  of  the  Triassic  rocks.     What  is  said  of  the 
localities  in  which  they  are  the  surface  rocks  ? 

238.  Why  is  this  system  often  called  in  Europe  the  Saliferous  sys- 
tem?    How  is  the  production  of  salt  there  in  contrast  with  its  pro- 


QUESTIONS.  345 

duction  in  this  country?  What  is  said  of  Triassic  plants?  What  of 
Triassic  coal  ?  How  did  the  atmosphere  differ  from  what  it  was  up 
to  the  Carboniferous  age  ?  What  animals  were  consequently  now 
introduced  ? 

239.  What  kinds  of  mammals  were  introduced  ?    What  kinds  of 
fishes  ?     What  is  said  of  the  Mollusks  ?    What  is  the  Lily  Encrinite  ? 
What  is  said  of  the  Keptiles  ?     Describe  the  Labyrinthodon. 

240.  What  is  said  of  the  name  Cheirotherium  ?    What  of  the  teeth 
of  the  Labyrinthodon  ? 

241.  What  of  the  tracks  of  Triassic  animals?     What  of  the  slab 
represented  in  Fig.  141  ?    What  of  the  Brontozoum  giganteum  ? 

242.  What  of  the  track  represented  in  Fig.  143  ?    What  of  the 
stone  fossil  book  ? 

243.  What  are  some  of  the  notable  localities  of  trap  rocks  in  this 
country  ?     As  they  were  thrust  up,  what  effect  resulted  in  the  adja- 
cent rocks?     What  is  said  of  their  systematic  arrangement? 

245.  What  is  said  of  the  vegetation  of  the  Triassic  period  ?     State 
the  facts  about  the  Portland  dirt-bed. 

246.  Give  in  full  what  is  said  of  the  animals  of  this  age. 

247.  What  were  the  most  prominent  of  the  mollusks  of  this  pe- 
riod?   What  is  the  class  to  which  they  belong,  and  what  are  the 
characteristics  of  the  class  ? 

248.  What  is  said  of  the  Ammonites?    What  of  the  Belemnites? 
What  of  the  Ichthyosaurus  ? 

249.  What  of  the  Plesiosaurus  ? 

250.  What  of  the  Pterodactyl  ?    What  has  been  the  common  opin- 
ion about  the  nature  of  this  animal  ?    What  is  Agassiz's  opinion,  and 
what  are  his  reasons  for  it  ? 

252.  What  is  probably  the  truth  about  the  flying  of  the  Pterodac- 
tyl ?     What  is  said  of  the  Dinosaurs  ? 

253.  What  are  the  rocks  of  the  Cretaceous  system  in  Europe  and 
Asia?     What  in  this  country?     What  is  said  of  the  Green-sand? 
What  of  chalk?     What  of  the  localities  of  the  Cretaceous  system  ? 

254.  How  was  chalk  formed  ?     Of  what  is  it  constituted  as  shown 
by  the  microscope  ?    What  is  said  of  chalk-marks  ?    What  is  the  act- 
ual difference  between  chalk  and  other  forms  of  carbonate  of  lime? 
What  is  said  of  deposits  of  chalk  now  going  on  ? 

255.  What  is  said  of  the  presence  of  flint  in  chalk?     What  of  the 
Xanthidia? 

256.  What  of  the  shell  prisms  in  flint?    What  of  the  flinty  spicula 
from  sponges  ? 

258.  What  of  the  agency  of  sponges  in  the  Cretaceous  period  ? 
What  of  the  animals  of  that  period  ?  What  of  the  change  in  the 
forms  of  the  Ammonites? 

P2 


346  QUESTIONS. 

259.  What  is  said  of  the  formation  of  mountains  at  the  close  of  the 
Reptilian  age,  and  in  the  age  after  it  ?     Give  in  full  what  is  said  of 
the  evidence  in  regard  to  this. 

260.  What  is  stated  about  the  heights  at  which  animal  remains  are 
found  in  the  mountains  raised  at  that  time  ?    What  is  said  of  the  de- 
struction of  life  at  the  end  of  this  age  ?    What  is  Hugh  Miller's  divi- 
sion of  the  life  of  the  earth  ?    What  is  said  of  new  creations  ? 

CHAPTER  XVIII. 

261.  In  the  age  of  Mammals,  how  was  the  condition  of  the  earth 
more  like  its  present  condition  than  it  was  in  the  previous  ages? 
What  is  meant  by  Cainozoic  time  ?     What  are  its  divisions  ? 

262.  What  is  said  of  the  terms  primary,  secondary,  and  tertiary  ? 
Give  in  full  what  is  said  of  Lyell's  division.     Of  what  kinds,  mostly, 
were  tertiary  deposits? 

263.  What  is  said  of  Tertiary  mediterranean  seas  ?     State  in  full 
what  is  said  of  the  Paris  basin.    What  is  said  of  the  areas  of  Tertiary 
deposits  ? 

264.  What  are  the  Tertiary  rocks?    What  is  said  of  some  of  the 
Tertiary  strata  of  Europe  ?     What  is  said  of  Nummulites  ? 

265.  State  in  full  what  is  said  of  the  Nummulitic  formation. 

266.  What  is  said  of  Tertiary  plants  ?     Give  in  full  what  is  said  of 
diatoms.    What  is  said  of  Tertiary  animals  ? 

267.  What  comparison  is  made  between  Tertiary  animals  and  those 
of  the  present  age  ?     What  is  said  of  the  fishes  ? 

268.  What  of  the  reptiles?    What  of  the  mollusks?     Give  the 
statement  about  the  arrangement  of  a  cliff  in  Virginia. 

269.  State  some  of  the  inferences  drawn  from  the  condition  of 
shells  in  strata.     State  in  full  what  is  said  of  indusial  limestones. 

270.  What  is  said  of  the  Mammals  of  this  age  ? 

271.  What  is  said  of  the  whale  called  Zeuglodon  cetoides  ? 

272.  To  what  class  did  the  most  prominent  of  Tertiary  mammals 
belong?     Describe  those  which  are  represented  in  Fig.  164.    What 
comparison  is  made  between  the  pachydermata  of  the  present  time 
and  those  whose  remains  were  found  in  the  Paris  basin  ? 

273.  What  is  said  of  Cuvier's  investigations  ?    To  what  conclusion 
did  he  come?     How  were  his  views  received?     State  in  full  what  is 
said  of  the  Dinotherium. 

275.  Indicate  the  extent  of  Tertiary  mountain-making.     Give  in 
full  the  comparison  between  the  Tertiary  mountains  and  those  made 
in  earlier  ages. 

276.  What  is  said  of  systems  of  rivers  ?    What  evidences  are  there 
of  the  working  of  volcanic  agencies  in  the  Tertiary  period  ?    What  is 
the  explanation  of  the  distinctness  of  some  of  the  cones  in  France? 


QUESTIONS.  347 

277.  What  is  the  name  of  the  highest  of  these  cones,  and  what  is 
said  of  it  ?     How  were  basins,  so  called,  formed  in  the  Tertiary  pe- 
riod ?    What  is  the  arrangement  of  the  London  basin  ? 

278.  How  do  artesian  wells  operate  in  such  basins?     What  is  said 
of  Tertiary  continent-making?     What  proportion   of  the  land  was 
brought  above  the  surface  of  the  water  in  this  period?     What  addi- 
tions were  made  to  North  America  ?     What  is  said  of  the  condition 
of  this  continent  at  the  end  of  this  period  ? 

279.  What  is  the  Post-tertiary  period  ?    What  was  to  be  done  in  it 
to  the  continents  ?    Into  what  three  epochs  is  it  divided  ?    What  was 
done  in  the  first  ?    What  in  the  second  ? 

280.  What  in  the  third  ?    Indicate  the  extent  of  the  reign  of  ice  in 
the  Glacial  epoch.     What  is  supposed  to  have  been  the  cause  of  the 
cold  ?     What  is  said  of  the  glaciers  of  this  period  ? 

281.  What  is  drift?     What  modified  drift?     What  are  the  two 
theories  about  drift  ?  »  What  is  the  truth  in  regard  to  them  ?    What 
changes  were  produced  by  the  drift  ?     What  change  in  the  Niagara 
River  ?     What  is  said  of  the  heights  at  which  drift  is  found  ? 

282.  What  is  said  of  the  shape  and  size  of  boulders  ?    What  of  the 
distances  to  which  they  have  been  carried?     What  examples  are 
given  of  the  transportation  of  them  across  deep  valleys  ?     What  is 
stated  about  the  distribution  of  boulders  ? 

283.  What  is  said  of  glacial  markings  ?    What  of  the  roches  mon- 
tonnees  ?    What  of  the  work  done  by  iceberes,  and  that  done  by  gla- 
ciers ?    What  of  the  localities  of  the  glacial  markings  ? 

284.  What  general  change  in  the  land  occurred  in  the  Champlain 
epoch  ?    What  resulted  from  this  change  ?    What  is  the  character  of 
the  formations  of  this  epoch  ?     How  are  boulders  situated  in  relation 
to  these  formations  ?     What  is  said  of  the  elevated  heights  to  which 
these  formations  sometimes  reached  ?     What  is  said  of  the  wide  dis- 
persion of  the  smaller  materials  of  the  drift  ? 

285.  What  are  the  river-plains  and  sea -beaches  of  the  Cham- 
plain  epoch  now  ?     What  is  said  of  the  subsidence  of  land  in  this 
epoch  ?    What  of  the  movement  in  the  Terrace  epoch  ?    What  effect 
was  produced  by  this  on  the  Champlain  strata?     To  what  is  the 
term  terraces  applied  ?     What  is  said  of  the  arrangement  of  ter- 
races ? 

286.  Describe  what  is  represented  in  Figs.  168  and  169.     State  in 
the  general  how  terraces  were  formed. 

287.  Explain  by  Figs.  170  and  171  the  manner  in  which  they  were 
commonly  made. 

288.  What  is  said  of  sea-beaches  ?     Describe  in  full  the  changes 
that  occurred  in  the  Niagara  River  in  the  Post-tertiary  period. 

289.  What  calculations  have  been  made  about  the  time  occupied 


.  ,      • 

348   -  QUESTIONS. 

in  the  recession  of  Niagara  Falls?     How  are  rivers  formed?    What 
two  things  are  needed  to  make  large  rivers  ? 

290.  When  were  the  grand  river  systems  of  the  earth  formed? 
What  is  said  of  the  alterations  in  the  terminal  moraines  of  the  an- 
cient glaciers  ?    What  of  the  results  obtained  in  their  investigation  ? 

291.  What  cities  are  built  on  moraines?    What  is  the  composition 
of  the  Post-tertiary  moraines  ?     What  is  said  of  the  present  conceal- 
ment of  their  character  ?     What  is  soil  ?     By  what  agencies  has  it 
been  made  ?     What  is  said  of  their  operation  in  the  Post-tertiary  pe- 
riod? 

292.  What  does  Hugh  Miller  say  of  the  preparation  of  soil  in  Scot- 
land in  that  period? 

293.  What  three  points  are  worthy  of  remark  in  regard  to  Post- 
tertiary  animals  ?    What  is  said  of  the  animals  of  England  of  that 
period  ? 

294.  How  did  the  Siberian  mammoth  differ  from  the  elephants  of 
the  present  time  ? 

295.  Give  in  full  what  is  said  of  the  covering  of  the  mammoth  in 
relation  to  the  question  of  climate.    What  is  said  about  vegetation  in 
reference  to  this  ?     What  is  said  of  the  abundance  of  mammoths  in 
certain  localities,  and  of  the  supply  of  ivory  from  their  tusks  ?    What 
is  stated  about  the  mammoths  of  this  country  ? 

296.  Give  the  history  of  the  St.  Petersburg  skeleton.     State  the 
speculations  about  it,  and  the  views  of  Cuvier. 

297.  What  is  said  of  the  mastodons?     How  do  their  teeth  differ 
from  those  of  the  mammoth  ?    What  is  said  of  the  Mastodon  gigan- 
teus? 

298.  What  is  the  Indian  tradition  about  mastodons  ?    What  is  sta- 
ted about  the  Newburg  mastodon  ?    "What  is  said  of  the  Mylodon  ? 

299.  What  is  said  of  the  structure  of  the  Mylodon's  skull? 

300.  What  is  said  of  the  Megatherium  ? 

301.  What  of  the  Megalonyx? 

302.  What  of  the  Glyptodon  ?    What  of  the  whales  of  that  period  ? 

303.  Where  have  caves  been  found  containing  bones  of  Post-ter- 
tiary animals  ?     Describe  the  Kirkdale  cave.     What  was  the  suppo- 
sition of  some  quarrymen  about  it  ? 

304.  State  in  full  the  results  of  Dr.  Buckland's  examination  of  this 


CHAPTER  XIX. 

305.  What  is  said  of  the  beginning  of  the  age  of  Man  ?    What 
about  its  conclusion  ? 

306.  Point  out  the  contrast  between  the  earth  now  and  in  the  Azoic 
age.     What  is  said  of  the  contrast  between  the  present  age  and  the 


QUESTIONS 


ages  following  the  Azoic  ?     How  was  the  Post-tertiary  period  the  most 
like  the  present  ? 

307.  What  facts  show  that  the  earth  was  essentially  completed 
when  man  was  introduced  ?    What  is  said  of  his  control  over  the 
earth  ?    Give  the  summary  of  the  changes  now  going  on  in  the  earth. 

308.  What  is  said  about  the  preservation  of  the  equilibrium  of  land 
and  ocean  at  the  present  time  ?     What  of  the  comparative  activity 
of  agents  of  change  now  and  in  former  ages  ? 

309.  What  is  the  distinction  between  the  historic  and  the  human 
period  ?    What  is  said  of  history  ?    What  of  the  study  of  the  remains 
of  a  people  ?    What  is  said  of  the  Stone  age  of  man  ?     What  of  the 
specimens  of  stone  implements  represented  in  Fig.  179  ?   What  of  the 
Bronze  age  ? 

310.  What  of  the  Iron  age  ?  What  of  literature  in  relation  to  these 
ages  ?    What  change  was  made  in  regard  to  the  animals  of  the  earth 
when  the  age  ofJMan  began  ? 

311.  Mention  some  of  the  animals  that  have  become  extinct  during 
the  age  of  Man,  and  state  what  is  said  of  them.    What  is  said  of  the 
evidence  that  man  is  one  species  ? 

313.  Of  what  nature  is  the  grand  difference  between   man  and 
other  animals  ?   In  what  respects  is  man  like  other  animals,  and  why? 
What  power  has  the  human  mind  which  the  brute  mind  has  not? 
Mention  the  various  results  of  the  possession  of  this  power.     What 
supposition  has  been  entertained  by  some  in  regard  to  future  prog- 
ress?   How  is  this  seen  to  be  unfounded? 

CHAPTER  XX. 

314.  Give  the  comparison  between  the  study  of  Astronomy  and 
that  of  Geology. 

315.  What  is  said  of  the  comparative  reliability  of  history  and  the 
record  of  the  rocks  ?    What  erroneous  idea  was  entertained  by  some 
in  the  infancy  of  geology  ?     What  is  said  of  the  authenticity  of  the 
two  records  of  creation  ?     What  of  apparent  inconsistencies  between 
them  ?    What  of  the  proper  mode  of  interpreting  the  Mosaic  record  ? 

316.  What  is  said  of  the  coincidences  between  the  two  records? 
What  is  said  to  show  that  the  account  of  Moses  was  divinely  inspired  ? 
What  is  said  of  the  propriety  of  noticing  the  record  of  the  Bible  in  a 
work  on  geology  ?   What  were  the  days  of  the  Mosaic  record  ?    What 
objection  to  the  view  taken  is  mentioned,  and  what  is  said  about  it  ? 

317.  What  are  the  various  senses  in  which  the  word  day  is  used  in 
the  Mosaic  account?    What  significant  fact  is  stated  about  the  use 
of  the  word  ?     Relate  the  English  legend  about  ammonites. 

318.  Relate  the  imposition  practiced  in  regard  to  this  legend.     Of 


350.-  QUESTIONS. 

what  use  is  geology  to  the  poet  and  the  painter?    What  is  said  of  a 
plan  in  the  formation  of  the  earth  ? 

319.  Give  the  comparison  in  regard  to  the  potter.     Illustrate  the 
fact  that  the  continents  were  constructed  each  on  its  own  plan.    What 
facts  show  that  the  Creator  had  a  plan  throughout  in  regard  to  the 
animals  of  the  earth  ?    What  is  said  of  time  in  geological  processes  ? 

320.  What  is   said  of  minute  agencies  in  the  formation   of  the 
earth's  crust  ?    What  of  disintegration  of  the  rocks  ?    What  of  the  ex- 
tent to  which  reconstruction  has  been  carried  on  in  the  formation  of 
the  earth's  crust  ? 

321.  What  have  been  the  two  purposes  of  disintegration  ?    Which 
is  the  principal  one  ?     How  has  diversification  of  the  earth's  surface 
been  effected  ?     Show  the  interplay  of  mechanical,  chemical,  and  vi- 
tal forces  in  the  case  of  carbonate  of  lime.    What  was  the  state  of  the 
atmosphere  before  the  Carboniferous  age  ?    What  change  was  effect- 
ed in  it  then,  and  with  what  result? 

322.  Show  how  the  interplay  above  referred  to  is  "illustrated  in  the 
making  of  coal  in  the  Carboniferous  age.    What  is  said  of  the  circu- 
lation of  matter  ?    What  has  been  the  notion  of  some  in  regard  to 
the  creation  of  the  earth  ?    What  is  the  truth  on  this  point? 

323.  What  is  said  of  the  creation  of  life  ?    What  of  the  notion  that 
there  has  been  no  creation  at  all  ?     State  the  development  theory. 
How  does  geology  show  this  to  be  false  ? 

324.  How  does  Page  state  the  changes  implied  in  this  theory? 
What  is  the  grand  creation  of  the  Deity  on  this  earth  ?    What  two 
facts  show  that  the  soul  of  man  was  a  distinct  creation  ? 

325.  If  mind  were  entirely  dependent  upon  matter,  what  ought  we 
to  find  in  the  brain  of  man  ?    What  is  said  of  the  doctrine  that  places 
man  onlv  a  little  above  the  monkevs? 


GLOSSARY. 


[The  numbers  refer  to  the  paragraphs  where  the  terms  are  explained.] 


Acephal 286 

Acrogens 250 

Amorphous 21 

Amphigens 249 

Amygdaloid 152 

Anhydrous 60 

Anticlinal 219 

Aqueous  (rocks) 211 

Arenaceous 145 

Argillaceous 145 

Atoll 238 

Azoic 261 

Bilobed 302 

Bort -35 

Brachiopod 286 

Cainozoic 261 

Calcareous 145 

Cenozoic 261 

Cephalopod 286 

Cleavage 24,  212 

Coal-measures 310 

Comprehensive  (type) 301 

Conformable  (strata) 222 

Cretaceous 339 

Ctenoid 299 

Cycloid 299 

Deliquesce 97 

Denudation 224 

Devonian 290 

Dimorphous 21 

Dip  (of  strata) 218 

Dodecahedron 25 

Dune 205 

Endogens 252 

Eocene 368 

Eremacausis 313 

Exogens 253 


Faults 223 

Ferruginous 113 

Flux , 69 

Fossiliferous 211 

Fossils 245 

Gangue 69 

Ganoid 299 

Gasteropod 286 

Gymnogens 251 

Haloid.... 95 

Hydrocarbon 46 

Indusial 379 

Joints  (in  rocks) 212 

Jurassic 339 

Lacustrine 369 

Lagoon 238 

Lamination 212 

Lode 231 

Massive  (minerals) 105 

Master-joints 212 

Mesozoic 261 

Metamorphic 211 

Miocene 368 

Nebulous  state 263 

Nummulite 239 

Octahedron 13 

Oolite 102 

Organized  (substances) ......      3 

Outcropping 220 

Paleontology 247 

Placoid 299 

Pliocene 368 

Primary  (forms) 25 

Protozoans 256 

Rhomb 25 

Saliferous 278 

Secondary  (forms) 26 


352 


GLOSSARY. 


Silurian 275 

Stratification 212 

Strike  of  strata 218 

Sub-carboniferous 311 

Synclinal 219 

Talus 185 

Tertiary , 368 


Trappean 

Trend 

Triassic 

Tufa 

Unilobed 

Water  of  crystallization. 
Weathering 


....  152 
....  162 

....  339 
....  195 
....  302 
....  20 
..  187 


INDEX. 


[The  numbers  refer  to  the  paragraphs.] 


Acephals 286 

Acrogens 250 

Adaptation 282 

JEpiornis  maximus 421 

Agate 114 

Ages,  boundaries  of 262 

Ages  of  Man,  Stone,  Bronze, 

and  Iron 420 

Aiguille  de  Dree 146 

Alabaster 60 

Albite 129 

Alg£e 249 

Alum 109 

Alumina 126 

Alumina,  phosphates  of. 110 

Alumina,  silicates  of 128 

Amber 45 

Amethyst 113 

Amianthus 125 

Ammonites 344,  352,  363 

Ammonium,  chlorid  of. 108 

Amorphons  minerals 21 

Amygdaloid 152 

Anoplotherium 382 

Anticlinal  lines 219 

Antimony 84 

Antimony,  sulphuret  of. 54 

Anthracite 39 

Anthracite,  how  produced....  315 
Anthracite,  introduction  of...  308 
Ants,  as  geological  workers..  235 

Aqueous  rocks 211 

Arenaceous  rocks 145 

Argillaceous  rocks 145 

Arsenic,  sulphurets  of 55 

Articulate 259,  332 

Asbestos...  ..  125 


Asphaltum 46 

Asterolepis 301 

Astronomy,    Geology    com- 
pared with 425 

Atmosphere,   relation   of  to 

coal 437 

Atolls 238 

Auvergne,  volcanoes  of 386 

Azoic  time 261 

Azoic  age,  heat  and  light  in  271 

Azoic  age,  land  of. 266,  267 

Azoic  age,  rocks  of 270 

Barrier  reefs 237 

Baryta,  sulphate  of. 62 

Basalt 152 

Basilosaurus 381 

Basins 387 

Belemnites 352 

Beryls 135 

Bismuth 87 

Bitumen 46 

Black  Jack 57 

Boracite 107 

Borax 99 

Boulders 393 

Brachiopods 286 

Breccia 143 

Brontozoum  giganteum. 346 

Bryozoa 284 

Buhrstone 150 

Cainozoic  time 261 

Cainozoic  time,  divisions  of. .  368 

Calamites 32 

Calcaire  grossier 369 

Calcareous  rocks 145 


354 


INDEX. 


Calcareous  spar 101 

Carbon,  diffusion  of 29 

Carbonic  acid 47 

Carbureted  hydrogen 48 

Carcharodon 376 

Caruelian 114 

Caverns , 216 

Cenozoic  time 261 

Cephalaspis 300 

Cephalopods 286 

Chain  coral 285 

Chalcedony 114 

Chalk 100 

Chalk,  flint  in 361 

Chalk,  source  of 360 

Chalk,  what  composed  of  239,  383 

Champlain  epoch 395 

Changes  in  the  earth,  agents 

of 172 

Cheirotherium 345 

Chlorite 123 

Chrome  yellow 75 

Chrysoberyl 135 

Cleavage 24,  212 

Clink-stone 152 

Coal 38 

Coal,  origin  of. 41 

Coal,  diffusion  of 44 

Coal,  localities  of 307 

Coal,  how  made 313 

Coal,  how  deposited 316 

Coal,  plants  in 319 

Coal,  rate  of  formation  of....  318 
Coal,  why  called  a  mineral...  42 
Coal  age,  vegetation  of  ..325,  326 

Coal  age,  climate  of. 327 

Coal  age,  scenery  of 328 

Coal  age,  animals  of 329,  334 

Coal  age,  North  America  at 

close  of 336 

Coal-fields 309 

Coal-measures 310 

Coal-measures,   disturbances 

in 337 

Coast-lines  of  Scotland 207 

Cobalt 85 

Coccosteus ...  ..  300 


Colorado,  canons  of 184 

Columnar  trap 153,  154 

Confervaj 249 

Conformable  strata 222 

Continent-making  in  the  Ter- 
tiary period 388 

Copper,  native 77 

Copper,  oxyds  of 78 

Copper,  carbonates  of 79 

Copper,  silicate  of 80 

Copper  of  Silurian  rocks  .....  277 

Coral  reefs 237 

Corals 236 

Corals  in  age  of  Coal 330 

Corals  in  Cretaceous  period..  363 

Corals  in  Devonian  age 293 

Corals  in  Jurassic  period 351 

Corals  in  Silurian  age 285 

Creation,  the  two  records  of.  427 

Creative  power 439 

Cretaceous  period,  animals  of  363 

Cretaceous  system 358,  359 

Crinoids  in  Coal  age 331 

Crinoids  in  Cretaceous  period  363 
Crinoids  in  Jurassic  period...  351 

Crinoids  in  Silurian  age 285 

Crust  of  the  earth,  floor  of...  264 
Crust  of  the  earth,  treasures 

in 170 

Crystallization 13 

Crystallization,      contrasted 

with  vital  growth 15 

Crystallization,  modes  of 19 

Crystallization,  water  of. 20 

Crystals,  arrangements  of..  16,  22 
Crystals,  primary  forms  of...  25 
Crystals,  secondary  forms  of.  26 
Crystals,  constancy  in  forms 

of 27 

Crystals,  symmetry  in 28 

Crystals,  sizes  of. 14 

Ctenoids 299 

Cuvier,  investigations  of. 247,  383 
Cycloids 299 

Decay fi 

Deliquescence 97 


355 


Deltas 177,  179 

Denudation 224,  225 

Deposits,  consolidation  of....  180 

Development  theory 440 

Devonian  age,  corals  in 293 

Devonian  age,  crustaceans  in  298 
Devonian  age,  mollusks  in...  297 
Devonian  age,  vegetation  in  295 
Devonian  age,  abundance  of 

fishes  in 303 

Devonian  age,  scenery  of....  305 

Devonian  age,  rocks  of 290 

Devonian  age,  United  States 

at  end  of 304 

Devonian  system 291,  292 

Diamonds 30-36 

Diatoms 240,  374 

Dikes 229 

Dimorphous  minerals 21 

Dinornis  elephantoides 421 

Dinosaurus 357 

Dinotherium 384 

Dip 218 

Dodo 421 

Dolomite 104 

Drift 232,  392 

Druidical  monuments 187 

Dunes 205 

Dutch  white 63 

Earth  as  a  whole 156 

Earth,  form  of 157 

Earth,  crust  of 158 

Earth,  ages  of 171 

Earth,  completion  of 416 

Earth  now  and  in  former  ages  415 
Earth,  stages  in  construction 

of 209 

Earth,  plan  in  construction  of  242 

Earth,  solidification  of 263 

Earth's    surface,    elevations 

and  depressions  in 160,  233 

Earth's  surface,  how  diversi- 
fied   169 

Earth  development,  plan  in..  431 

Earth's  crust,  floor  of. 264 

Earth's  history,  divisions  of..  261 


Earthquakes 200,201 

Earth-worms   as    geological 

workers 235 

Ehrenberg  on  chalk 239 

Elevations 233 

Emeralds 135 

Emery 126 

Endogens 252 

England,    post-tertiary   ani- 
mals of. 404 

Eocene i 368 

Epsom  salts 61 

Eremacausis 313 

Etna 196 

Exogens 253 

Faults 223,225 

Feldspar 129 

Ferns  in  coal  strata 323 

Fingal's  Cave 153 

Fishes 299 

Fishes  of  age  of  Coal 333 

Fishes  of  Tertiary  period 376 

Fishes,  tails  of 302 

Flexures  of  rocks 214 

Flint,  fossils  in 362 

Flint  in  chalk 361 

Flood-plain 174 

Fluor  spar 105 

Fluxes 69 

Foraminifera 239 

Fool's  gold 50 

Formation 212 

Fossils 245-247 

Fossils,  animal 255 

Fossils,  vegetable 254 

Fossil  book  in  stone 347 

Fossiliferous  rocks 126 

Franconia  Notch 395 

Fringing  reefs 237 

Fungi 249 

Galena 52 

Gangues 69 

Ganoids 299 

Garnets 131 

Gar-pike 333 


356 


INDEX. 


Gasteropoda 186 

Geological  evidence,  nature 

of 210,  244 

Geysers 203,  204 

Giant's  Causeway 153 

Glacial  period 368,  391 

Glacial  markings 394 

Glaciers 188-190 

Glance,  copper 51 

Glauber's  salt.. 61 

Gneiss , 148 

Graham's  Island 199 

Granite 146,  147 

Graphite 37 

Green-sand 358 

Green-stone 152 

Gold 91-93 

Goppert,  experiments  of. 319 

Grotto  del  Cane 47 

Gulf  Stream 168 

Gymnogens 251 

Haloid  salts 95 

Hamburg  white 63 

Heat,  agency  of. 193 

Heat,  relation  of  to  forms  of 

matter 2 

Hematite 74 

Herculaueum 195 

Historic  period 419 

Hornblende 125 

Human  period 419 

Hydrozoa 284 

Hyla3osaur 357 

Icebergs 191 

Iceland  spar 101 

Icononzo,  natural  bridge  at ..  216 

Ichthyosaurus 353 

Iguanodon 357 

Indusial  limestones 379 

Iridium 94 

Iron,  ores'of 70 

Iron,  meteoric 71 

Iron,  carbonate  of 76 

Iron  mountains -73 

Islands,  volcanic ,  199 


Joints 212 

Jupiter  Serapis,  Temple  of..  206 
Jurassic  period,  plants  of....  349 
Jurassic  period,  animals  of...  351 

Kaolin 129 

Kilauea,  Crater  of 197 

Kirkdale  Cave 413 

Labradorite \ 119 

Labyrinthodon 345 

Lagoons 238 

Lakes 166 

Lakes,  deposits  in 176 

Lamination 212 

Land,  arrangement  of. 161 

Land,  proportion  of  to  water.  159 

Lapis  lazuli 134 

Laurentian  Hills 385,  388 

Lead 81 

Lead,  oxyds  of 81 

Lead,  sulphuret  of 52 

Lead,  sulphate  of 59 

Lepidodendron 322 

Lepidosteus 333 

Levels,  alterations  of 206 

Life  introduced  by  the  Cre- 
ator     15 

Life  in  different  ages 243 

Life,  dawn  of,  in  the  earth...  273 
Life,  plan  in  structures  of....  248 

Life-record  in  the  rocks 243 

Life-record,  Palaeozoic 338 

Lily  Encrinite 344 

Lime,  carbonate  of. 100 

Lime,  silicates  of 119 

Limestone 100 

Lingula 28G 

Lisbon,  earthquake  at 201 

Lithodomes 207 

Loggan  stones 187 

London  basin 387 

Lowlands 164 

Magnesia,  salts  of. 107 

Magnesia,  silicates  of 120 

Magnesia,  sulphate  of 61 


INDEX. 


357 


Magnesian  carbonate  of  lime  104 

Magnetic  iron  ore 71 

Mammals 260 

Mammals  of  Tertiary  period  380 
Mammals  of  Triassic  period  344 
Mammoth  Cave  of  Kentucky  16 

Mammoths 405 

Man,  creation  of 441 

Man,  changes  made  by 208 

Man  one  species 422 

Man's  place  in  nature 423 

Manganese 88 

Marble .  102 

Master-joints 212 

Mastodons 408 

Matter,  circulation  of. 438 

Matter,  forms  of. 2 

Megalonyx 410 

Megalosaur 357 

Megatherium 410 

Mercury 89 

Mercury,  sulphate  of. 56 

Metamorphic  rocks 211 

Mesozoic  time 261 

Mica 130 

Microscopic  animals  in  rock  339 

Minerals,  forms  of. 1 

Minerals  in  living  substances    17 
Minerals,   simple  and  com- 
pound        9 

Mines,  salt 98 

Minium 81 

Miocene 368 

Mollusks 258 

Mollusks  in  age  of  Coal 334 

Mollusks  in  Cretaceous  pe- 
riod  363 

Mollusks  in  Devonian  age  ...  297 

Mollusks  in  Silurian  age 286 

Mollusks  in  Tertiary  period..  378 

Moraines 188,  190,  402 

Moraines,  cities  built  on 402 

Mosaic   record,  authenticity 

of 427 

Mosaic  record,  days  in 428 

Mountain-making  in  Tertiary 
period 385 


Mountains,  arrangement  of..  162 

Mountains,  how  made 226 

Mountains,    relation    of,    to 

fertility 167 

Mylodon 409 

Naphtha 46 

Nautilus 286 

Niagara  Falls,  recession  of...  183 
Niagara  River,  changes  in  392, 399 

Nickel 86 

Nummulites 239 

Nummulitic  formation 372 

Oaze 239 

Obsidian 155 

Olivine 152 

Onyx 114 

Oolite 102 

Opal 115 

Ores 66-68 

Organic  agencies 207 

Organized  substances 3 

Orpiment 55 

Orthoceras 286 

Osmium 94 

Oxysalts 95 

Pachydermata    of   Tertiary 

period 382 

Pala30therium 382 

Palaeozoic  time 261 

Palisades 154 

Peat 43 

Pebbles 234 

Permian  period 335 

Petrifactions 118 

Petroleum 46 

Pitchstone 155 

Placoids 299 

Plateaus 164 

Platinum 48 

Plesiosaurus 354 

Pliocene ,...." 14 

Pompeii 195 

Porphyry 152 

Portland  dirt-bed ...  ,..  350 


358 


INDEX. 


Post-tertiary  period 368,  389 

Post-tertiary  period,  divisions 

of 390 

Post-tertiary  period,  animals 

of 404 

Post-tertiary  period,  length  of  400 
Post-tertiary  period,  rivers  of  401 

Potosi,  situation  of., 164 

Primary  forms  of  crystals....  25 

Protogine 146 

Protozoans 256 

Pterichthys 300 

Pterodactyl 355,  356 

Pudding-stones 143 

Pulpit  Rock 182 

Pumice 155 

Pyramids,  of  what  rock  built  239 

Pyrites,  iron 50 

Pyrites,  copper 51 

Pyroxene 124 

Quartz 113 

Quartz  rock 150 

Quito,  situation  of 164 

-Radiates 257 

Realgar 55 

Reconstruction 435 

Red  lead 81 

Reptiles  of  age  of  Coal 333 

Reptiles  of  Tertiary  period  ..  377 
Reptiles  of  Triassic  period...  345 
Reptilian  age,  destruction  of 

life  at  close  of. 365 

Reptilian  age,  uplifts  at  close 

of 364 

Rhodium 94 

Richmond,  white  clay  of. 240 

Ripple  marks 210 

Ripple  marks  on  Silurian 

beach 280 

Rivers,  amount  of  deposits 

from 178 

Rivers,  deposits  in 174 

Rivers,  improvement  of 175 

Rivers  of  post- tertiary  period  401 
Rivers,  systems  of 165 


Roches  montonnees 394 

Rock,  definition  of 138 

Rocks,  disintegration  of. 434 

Rocks,  elementary  substances 

in 139 

Rocks,  kinds  of 140-145,  211 

Rocks,  order  of  succession  of  21-3 
Rocks,  regularity  of  form  in..  23 
Rubies 126,  127 

Salt  mines 98 

Salt  of  Triassic  system 342 

Saltpetre 96 

Salt  springs 98 

Sand 234 

Sand  moved  by  wind 205 

Sandstones 151 

Sapphire 126 

Satin  spar 60,  101 

Schists 149 

Scoria 155 

Sea-beaches 398 

Secondary  forms  of  crystals..  26 

Serpentine 122 

Shales 149 

Shells  in  rocks 239,  246,  258 

Shells,  silicious 240 

Sigillaria 321 

Silica 112 

Silica  in  solution 116 

Silica  in  two  states 117 

Silica,  petrifactions  with 118 

Silicates Ill 

Silicious  rocks 145 

Silurian  age,  climate  of....;..  288 

Silurian  age,  life  in 281 

Silurian  age,  subsidences  and 

elevations  in 289 

Silurian  beach 280 

Silurian  copper 277 

Silurian  salt 278 

Silurian  shales,  carbonaceous 

matter  in .^-283 

Silurian  system,  distribution 

of 276 

Silurian  system,  rocks  of.....  274 
Silver 00 


INDEX. 


359 


Silver,  sulphuret  of 52 

Slates 149 

Smalt 85 

Soapstone 121 

Soda,  borate  of 99 

Soda,  nitrate  of 97 

Soda,  sulphate  of 61 

Soil  made  in  post-tertiary  pe- 
riod  403 

Soil,  what  it  is 234 

Solfataras 202 

Sphinx,  what  made  of 239 

Spicula  in  flint  nodules 362 

Spinel 127 

Stalagmites  and  stalactites...  103 

Stigmaria 321 

Strata 212 

Strata  at  different  angles 217 

Strata,  conformable  and  un- 

conformable 222 

Strata,  flexures  of 214 

Strata,  mapping  of. 220 

Strata,  measuring  of 221 

Strata,  upheavals  of. 216 

Stratification 212 

Stratified  rocks 144 

St.  Petersburg  skeleton 406 

Strike 218 

Sub-carboniferous  period 311 

Subsidences 233 

Sugar,  crystallization  of. 18 

Sulphur 49 

Sulphurets 50-57 

Sulph  ureted  hydrogen 64 

Sulphuric     and    sulphurous 

acids 63 

Syenite 146 

Synclinal  lines 219 

Talc 121 

Talus 126 

Terrace  epoch 396 

Terraces,  how  formed 397 

Tertiary  period 368 

Tertiary  period,  deposits  of..  369 
Tertiary   period,   mountains 
made  in  ...  ..  385 


Tertiary    period,    pachyder- 

mata  of. 382 

Tertiary  period,  plants  of 373 

Tertiary  period,  rocks  of 371 

Time  in  geology 432 

Tin 82 

Tomboro 198 

Topaz 126,  133 

Tourmaline.. 132 

Tracks  as  evidences  in  -geol- 
ogy   210 

Tracks  in  Triassic  rocks 346 

Trachyte 152 

Trap  rocks 152-154,  348 

Trap  rocks,  how  formed.. 229,  230 

Trap  scenery 229 

Triassic  period 339 

Triassic  rocks 330 

Triassic  plants 343 

Triassic  salt 342 

Triassic  animals 344 

Trilobites 287 

Trilobites  of  age  of  Coal 332 

Tufa 195 

Turquois 119 

Unconformable  strata 222 

Under-clay 310 

Unstratified  rocks 144,  211 

Valleys,  kinds  of 227 

Venice  white 63 

Ventriculites 361 

Veins 231 

Verd-antique 122 

Vertebrates 260 

Vesuvius 195 

Viesch,  glacier  of 388 

Vitriols 58 

Volcanoes 163,  194 

Volcanoes,  formation  of 228 

Volcanoes  of  the  Tertiary  pe- 
riod   386 

Water  as  a  leveler 192 

Water  changing  locality  of 
materials ..  173 


360 


INDEX. 


Water,  chemical  action  of....  186 

Water,  circulation  of 168 

Water  encroaching  on  land..  181 
Water,  erosive  power  of..  182,  184 
Water,  proportion  of  land  to  159 

Weathering 187 

Whales  of  post-tertiary  period  412 
White  lead...  .  81 


Xanthidia...  362 


Zaffre 

Zeuglodon  cetoides 

Zinc 

Zinc,  sulphuret  of.. 

Ziphodon 

Zircon 


85 

381 

83 

57 

382 

136 


THE   END. 


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